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00:00We are surrounded by extraordinary feats of engineering, constantly pushing the boundaries of what's possible.
00:10Without engineering, there'd be no modern world.
00:13Gigantic cities, amazing infrastructure, and ingenious inventions.
00:20Engineering is the key to turn dreams into reality.
00:24To reach these dizzying heights, today's technology relies on breakthroughs made by ancient engineers.
00:31It's mind-boggling how they did this.
00:34How did early civilizations build on such a scale?
00:38They raised the bar for construction in a way that no one thought possible.
00:43The sheer engineering ability that is in itself impressive.
00:47By defying the known laws of physics, and daring to dream big, they constructed wonders of the world.
00:56From gigantic pyramids, to awe-inspiring temples, and mighty fortresses.
01:05All with the simplest of tools.
01:07I cannot imagine the skills people would have needed to build like this.
01:11Now, it's possible to unearth the secrets of the first engineers.
01:19They managed to construct edifices that have survived the ravages of time.
01:24And reveal how their genius laid the foundations for everything we build today.
01:41Humanity is obsessed with surpassing the limits of construction and engineering.
01:48Establishing new records, only to break them again and again.
01:53As humans, we always want to advance.
01:57As engineers, always want to push the boundaries.
02:01Every decade sees radical new structures.
02:05And bigger is always better.
02:08Rising a dizzying half a mile above the desert, Dubai's Burj Khalifa currently reigns as the tallest structure in the world.
02:19Wrapped in a glass curtain wall, the supertower's sleek silhouette dwarfs the surrounding city.
02:28And in Ontario, the absolute towers appear to shimmer and twist around their own axis.
02:34With continuous balconies and elliptical floor plans, the skyscrapers take on shapes that seem to defy the laws of physics.
02:47But these architectural monuments also express the wealth and power of those who commissioned them.
02:54They are expensive and they're always symbols of power to a certain extent.
02:59Engineering as the ultimate status symbol.
03:02They want to build the biggest thing they can do to make a point of saying, I was here.
03:12Creating massive, eye-catching structures is one of the best ways to impress.
03:17Whether they're captivating onlookers.
03:21Or symbolizing the might of a nation.
03:24These statement buildings are found across the globe.
03:29Reaching ever higher.
03:31We certainly see it going on today.
03:33The race to be the tallest building in the world.
03:35But while modern tall buildings are usurped by a new rival every few years.
03:41In the ancient world, one civilization built a structure that would reign supreme.
03:47For almost four millennia.
03:49In terms of building big, tall structures, I don't think anyone rivaled the Egyptians.
04:07What the Egyptians did was take monumental buildings to its extremes.
04:13Egypt's most iconic structure became the tallest building in the world.
04:18A title it retained for more than 3,500 years.
04:23The Great Pyramid of Giza.
04:26The largest pyramid ever built.
04:28Last of the original seven wonders of the world still standing.
04:33It was recognized by the ancient world as extraordinary.
04:43And it's still an iconic symbol of Egypt and of the ancient Egyptians today.
04:50At a time when most buildings were only one story high, the Egyptians created something unimaginable.
04:57Soaring to over 475 feet, the pyramid remained the world's tallest structure until the 14th century.
05:04It's the biggest ancient building of them all.
05:08It's still standing.
05:10And it's a real icon.
05:13But the Great Pyramid isn't only about scale.
05:16With principles that still apply today, it's also a masterpiece of mathematics and precision engineering.
05:24A line to face true north with pinpoint accuracy.
05:29This size makes it impressive, but it's also the dimensions, the proportionality.
05:33The measurements are very accurate.
05:34Each side is equal.
05:36Built with over 2 million stone blocks.
05:41Some seem to weigh as much as two and a half tons.
05:44And these fit together like a jigsaw puzzle.
05:47The expertise that went into making this thing was incredible.
05:51It's a triumph against impossible odds.
05:55Believed to have been constructed in just 20 years.
05:58The result of extraordinary human ingenuity.
06:01It's built in such a carefully engineered way that it seems impermeable to the passage of time.
06:09It's a solid structure, built on solid foundations, built to last, which indeed it has.
06:14The Great Pyramid is an ancient engineering masterpiece.
06:18But this world-famous monument is still shrouded in mystery.
06:26For centuries, it has remained one of the great engineering enigmas.
06:30The complex engineering that went into that, without the modern-day technology that we have, is really astounding.
06:39The kind of challenges just to build something of that scale, with the materials they had available, is really an amazing feat of engineering.
06:47What drove the Egyptians to erect such enduring monuments in the first place?
06:53Of course, there are many theories as to why the pyramids were constructed by the ancient Egyptians.
07:00Were they really enormous burial places, with hidden chambers inside?
07:06Or did they serve another function?
07:08Even the ancient Egyptians looked back, generations later, at this thing with some degree of mystery.
07:17To find answers, we need to go back to the first pyramids.
07:21Over 5,000 years ago, Egyptian civilization began to emerge along the banks of one of the world's longest rivers.
07:41The Nile.
07:43For the ancient Egyptians, the Nile was fundamental to their entire culture.
07:47Without the Nile, there is no Egypt.
07:49Annual floods brought nutrient-rich waters to the lands along the Nile's banks, giving life and fertility.
07:59It's that that could support this great civilization and allow it to store grain and grow and grow and grow and grow and do more and more remarkable things.
08:09For the most part, it was a blessing, and Egypt became a land of plenty.
08:14But during times of drought, there was starvation and death.
08:23If the Nile flood was too low, then famine would follow.
08:28If the Nile flood was too high, then entire villages could be washed away.
08:33This precarious existence led to an obsession with death and the afterlife.
08:40And in order to protect the bodies of their dead, the Egyptians developed a method of artificial preservation.
08:50Mummification.
08:52Mummification was invented to provide a permanent physical home for the soul which could wander around, live forever, and then come back at will into its body.
09:01The body of the deceased was washed and purified.
09:08All the organs were removed, excluding the heart.
09:12It was then dried out with salts and wrapped head to toe, before finally being laid to rest.
09:20Some bodies were simply wrapped in linen and put in the desert.
09:23The desert sands may have been good enough for ordinary Egyptians, but their mummified rulers demanded a more secure resting place.
09:32The ancient Egyptian king was essentially worshipped as a kind of god in life and certainly as a god in the afterlife.
09:41Workers used simple hand tools, excavating huge underground burial chambers for their kings.
09:49Protective tombs for their journey into the afterlife.
09:56And mummification continued for thousands of years.
10:01But other techniques for preserving the human body after death have since been invented.
10:10Including one very recent innovation.
10:13Hundreds worldwide have had their corpses frozen in special cryogenic chambers.
10:23Preserving their remains in the hope that resurrection may be possible in the future.
10:30People hope that when they're eventually brought back to life, that there will have been advances in medicine that means they'll be able to treat incurable diseases that we have today.
10:40The procedure must begin minutes after death.
10:45Antifreeze compounds replace the corpse's blood to prevent harmful ice crystals forming.
10:51As the body is slowly cooled to a temperature of minus 320 degrees Fahrenheit.
10:59And finally lowered into a tank of liquid nitrogen.
11:04Where it remains.
11:07Ready for the afterlife.
11:10But over 4,000 years ago, all the ancient Egyptians had was their belief in the king.
11:24And they were certain the efforts their engineers made to preserve the royal body would be rewarded.
11:30Each royal mummy had to be buried in a very, very safe place.
11:35And it was only when this was done could Egypt truly thrive.
11:39Because it was believed that each successive pharaoh contained divine power.
11:45By creating a secure burial chamber for the king, the people believed that the survival of their civilization was ensured.
11:52So royal grave sites became unmissable monuments.
11:57The earliest kings were buried in what we call master platoons.
12:01Low rectangular structures with sloping sites.
12:05They can be quite large, but they weren't made from stone.
12:08These were made from mud brick.
12:10Mud brick was the most common building material in Egypt because simply it's made of the mud from the banks of the Nile.
12:20But a belief in the afterlife wasn't the only motivation for tomb building.
12:25Each successive ruler wanted a memorial larger and grander than the last.
12:30But royal tombs had become a mark of status.
12:36Then, around 2650 BC, one genius of ancient engineering had an outlandish, world-changing idea.
12:47To take tomb building to new heights.
12:52King Joseph had his architect, Imhotep, embellish his simple Mastaba tomb.
12:58You can see a really big leap from the previous phase.
13:03This huge leap that Imhotep seems to make.
13:06One that would change the Egyptian landscape forever.
13:11Imhotep wanted something grander to commemorate his king and took Egyptian engineering to the next level.
13:19Literally.
13:20He envisioned six different layers of Mastaba stacked on top of each other.
13:24But this new design would involve a tremendous amount of material and weight.
13:30So a radical breakthrough was needed.
13:33The great leap forward was that the Joseph's pyramid was built of limestone rather than mud brick.
13:39The use of stone revolutionized construction in Egypt.
13:46The architect, Imhotep, also changed the design.
13:50Instead of the rectangular Mastaba, it was made into a square, which is effectively far more stable.
13:59Imhotep had designed Egypt's first pyramid.
14:02It would prove a massive undertaking.
14:07Building the stone is not easy.
14:08It's not cheap.
14:09It takes a long time.
14:10It's not an easy material to work with.
14:13Over the course of Djoser's nearly 20-year reign, his builders assembled the six stone layers of his pyramid.
14:19A colossal structure, unlike anything the Egyptians had ever laid eyes on.
14:24Djoser's pyramid is probably the world's first monumental building in stone.
14:30This engineering masterpiece reinforced the king's status as a living god.
14:40196 feet tall, the groundbreaking form would come to be known as a step pyramid.
14:47It can only be imagined what impact this first pyramid must have had on the Egyptian population.
14:55The whole structure was designed to be seen from the valley below.
15:00Imhotep would go down in history as the world's first engineer and architect, known by name.
15:12He had created the original skyscraper.
15:20Some modern architects have also become household names.
15:24One of the greatest in their ranks is Frank Gehry.
15:32His buildings are monumental works of art.
15:36He has such a signature style to him that you can pretty much look at a building and probably guess correctly that that's a Gehry.
15:47Cutting-edge technology helps deliver the engineering solutions that bring Gehry's sculptural sketches to life.
15:56For me, it's about his use of geometry to create really, really unusual shapes.
16:02In a sense, he was a bit like the Egyptians who built the pyramids as they were making things that would make people go, wow, look at that.
16:11Gehry is an architect who refuses to accept limits, something he and Imhotep appear to have in common.
16:31But why was the step pyramid design chosen for Djoser's tomb?
16:41Some believe that the pyramid's sides act as a celestial staircase, guiding the pharaoh's soul to the afterlife.
16:50Or could Imhotep have had a more practical reason?
16:54If one looks at the grains of sand trickling through an hourglass, they naturally form a pyramidal shape.
17:01And that's because the pyramid is a deeply stable structure.
17:06And a stable structure is a strong structure.
17:09A pyramid is very stable because of having a large base compared to its height.
17:14You've got basically a very low centre of gravity.
17:17It's a structure that, as long as you expand the base, can grow infinitely large because the base will sustain the structure as far as you want.
17:29Their stable form explains why the pyramids of Egypt are still standing tall, enduring weather and erosion over millennia.
17:41Djoser's step pyramid launched an engineering arms race that would continue for centuries.
17:48After Djoser, the pyramid became the kind of stereotypical monument in which a king would be buried.
17:56They were really showing off the might and power of the Egyptian empire at the time.
18:03We do the same thing today.
18:05People build taller and taller.
18:08But as with everything in the modern world, even big buildings need to be put up as quickly as possible.
18:15In New York City, marvels of engineering continue to be developed.
18:21High-profile skyscrapers, many of which reach 1,000 feet tall.
18:26With more and more commissioned each year, the scale of this new wave of construction is unprecedented.
18:34And thanks to modern materials and techniques, each building can be completed within a few years.
18:40In ancient Egypt, pyramids couldn't possibly be built this fast.
18:57But the pressure was on.
19:00Not only to be ready for the death of the pharaoh, but to go taller than before.
19:05There was this real desire to exceed what your predecessor had done.
19:10There is a kind of mark of your status, of your ability.
19:14Pushing pyramid construction to the next level called for new architectural and engineering skills.
19:21Djoser's successors must have seen Djoser as a very hard act to follow.
19:26Most of them had very short reigns, and of course you can't achieve much if you're only on the throne for two or three years.
19:33In fact, for the next several decades, not a single pyramid was built successfully.
19:40Until one pharaoh changed ancient engineering forever.
19:44In the fourth dynasty of ancient Egypt, King Sneferu was determined to build a pyramid far larger than his predecessors.
19:55Blinded by ambition, his monument was destined to meet with terrible disaster.
20:01Sneferu began constructing the Pyramid of Maidun.
20:05A steppe pyramid similar in design to the original, but significantly taller.
20:09But halfway through construction, the steppe design was mysteriously abandoned.
20:16It seems that the king had a desire to smooth the sides, to create the true pyramid.
20:22The king asked that his workers fill in the steppe with limestone, and then apply smooth casing to the outside.
20:31It was a revolutionary concept, but something went terribly wrong.
20:35Modern archaeology has revealed that the outer layer of limestone rested on sand, rather than solid rock.
20:43It put the bases of the four external supporting walls under enormous pressure.
20:49Something had to give.
20:51Unfortunately, at some point, probably during construction, these sides began to crumble away.
20:59As if in anticipation of defeat, the king had already begun construction on his next pyramid.
21:17It's a much larger construction than the previous pyramid, and that's going to come with a whole bunch of challenges.
21:23But as his new pyramid grew skyward, Sneferu found himself once again on the brink of disaster, and construction ground to a halt.
21:35They might have thought that the amount of stone that was going to be needed to complete this thing,
21:40and the height that it was going to get to, was just going to be too much.
21:44Without a drastic design change, the pyramid couldn't be completed.
21:48Determined not to disappoint their king, Sneferu's engineers changed the angle of the upper section from the original 54 degrees to a much shallower 43,
22:00a modification that would significantly reduce the volume and weight of the pyramid's upper half.
22:06The compromise worked, but it came at a cost.
22:10In saving the structure, the engineers produced the strange, comical shape in evidence today.
22:20It's gone down in history as the bent pyramid.
22:29Last-minute modifications are still commonplace in construction.
22:34Most are only minor, though there are exceptions.
22:40In 1971, the John Hancock Tower in Boston was mid-construction when something unexpected happened.
22:55Glass began smashing onto the streets below.
23:00To the engineers' horror, the reflective windows were falling out of the building.
23:05There was too much movement taking place, and so the stresses in the glass were causing these windows to break and actually pop out of the building.
23:16Over 10,000 window panes had to be replaced with heat-treated panels.
23:22This new glass had to be processed through a furnace to significantly increase its strength,
23:29providing greater resistance to thermal and mechanical stresses.
23:35But replacing the old windows was a long and costly process.
23:40This is one of the challenges of these prominent buildings.
23:44They're in the public eye as they're being constructed,
23:47and so any mistakes that happen are very public and very embarrassing.
23:51Before the new panels could be installed,
23:54the empty frames were covered up with sheets of plywood,
23:59earning the tower the nickname
24:00Plywood Palace.
24:02Errors like this are hard to ignore.
24:12And despite reaching over 220 feet tall,
24:16Sneferu appears to have seen his bent pyramid as a failure.
24:20But the king and his engineers learned from their mistakes,
24:24and moved on to a third attempt.
24:28They now knew that large, high-quality blocks of limestone would strengthen a pyramid's foundation.
24:35And a wider base with a shallower angle of incline would increase its stability.
24:41It is 43 degrees, like the top part of the bent pyramid, from the base.
24:44So it's a very low-lying pyramid.
24:47After decades-long attempts, Sneferu had finally achieved the perfect pyramid form.
24:54Engineering genius had triumphed against all odds,
24:58creating the first success of a new breed.
25:03The Red Pyramid.
25:10It's what you call a perfect pyramid.
25:12The one that conforms to what we think of as a pyramid the most.
25:19The smooth and symmetrical shape recognized worldwide.
25:23And at 229 feet tall, Sneferu's monument would be a tough act to follow.
25:33But this remarkable structure didn't mark the zenith of pyramid building.
25:43Sneferu's son Khufu would in turn dream the unimaginable.
25:47Determined to be remembered as one of Egypt's greatest rulers.
25:53In the 26th century BC, one of his first decisions as pharaoh
25:58was to commission his own grand tomb.
26:02This was intended to be a new pyramid on a totally different scale.
26:06There was an element of wanting to build bigger and better than his father.
26:11It was down to him to excel the king that went before.
26:15Could it even be done?
26:19Planned to cover an area more than 12 acres,
26:22Khufu's pyramid would require more than 2 million stone blocks to complete.
26:27Adding up to a total of 6.5 million tons.
26:31More than 17 times the weight of the Empire State Building.
26:36And accuracy of form and measurement were of paramount importance to Khufu's architects.
26:42One small error at the base would lead to a complete disaster closer up to the top.
26:47So the alignment and accuracy of placing every single block as they went was critical.
26:55Creating such a monumental masterpiece would demand tens of thousands of workers.
27:00But would Khufu's Great Pyramid be built by an army of slaves or willing laborers?
27:06For years, controversy raged.
27:14Then, in 2010, mud-brick tombs were discovered near the Great Pyramid.
27:21More than 4,000 years old.
27:24These shafts contained the skeletons of pyramid builders, well-preserved by the dry sand.
27:29Along with clues to how the workers were treated in life.
27:36They were provided with food for the next world.
27:38They were provided with the kinds of beer and bread that they'd enjoyed in this world.
27:43And some of the tombs even have inscriptions on them telling us who was buried inside, what job they did.
27:50The tombs provide strong evidence that the Great Pyramid was built by skilled construction workers, highly regarded for their craft.
28:00Not a disposable workforce of slaves.
28:06They may have been willing workers, but a monumental job still lay ahead.
28:11To build something like the pyramids, you've got to organize the movements of massive amounts of material, the creation of the blocks that you need.
28:23Cutting the rock would be a Herculean task for laborers equipped only with copper chisels and crude hammers.
28:32The sheer physicality of this kind of work, the physical toll that must take on the body, would have been immense.
28:38Theories suggest that up to 20,000 workers toiled on the Great Pyramid, consuming vast quantities of raw materials.
28:53Since Khufu's reign, demand for natural resources has grown exponentially.
29:03Quarrying now takes place on an industrial scale.
29:06Reaching far deeper than the Egyptians ever imagined possible.
29:12Modern day quarries and mines are enormous undertakings compared to ancient predecessors.
29:20Two and a half miles wide and three quarters of a mile deep.
29:24Bingham Canyon, outside Salt Lake City, is considered the largest mine on Earth.
29:29It's also one of the most productive.
29:32As of 2018, Bingham Canyon generated approximately 19 million tons of copper.
29:42More than any other mine in history.
29:47The sort of machinery that's used on them is pretty terrifying, actually awe-inspiring.
29:54Bucket wheel excavators, capable of moving millions of cubic feet every day.
30:00Equivalent to more than 20,000 fully loaded dump trucks.
30:07We might go and doff our caps at the Egyptians for their pyramids.
30:11If they were to see our quarries in our mines, they would doff their caps in return.
30:18Mining was a much slower business in ancient Egypt.
30:21Even once stone had been extracted, another great challenge remained.
30:28Transporting it to the build site.
30:31A recent discovery has revealed exactly how it was done.
30:35In 2013, a team of archaeologists came across something remarkable, hundreds of miles from the pyramid site at Giza.
30:44Dozens of inscribed papyrus fragments, written more than 4,500 years ago, during the reign of Khufu.
30:54These are essentially a logbook.
30:57What they tell is a foreman called Mera, and he's commanding a ship, ferrying goods from one part of Egypt all the way up to the Giza necropolis, where the pyramids are built.
31:08Mera recorded his daily activity transporting stone by boat, from the Tura limestone quarry to Giza.
31:19Varying blocks from this quarry, and others along the Nile, ensured enough stone reached the pyramid site.
31:27All thanks to a mode of transport on which the modern world still depends.
31:38Cargo ships carry billions of tons of goods across the globe each year.
31:44And that number continues to rise.
31:47We've become very used to the idea of containerized transport, and it affects how we move stuff around the world.
31:56Container ships reach up to 1,300 feet in length, capable of carrying over 100,000 tons in a single journey.
32:08Thanks to their shipping skills, the ancient Egyptians maintained a steady supply of blocks to the pyramid site.
32:19But the biggest challenge still lay ahead.
32:23How do you get that block that you've quarried and put next to the pyramid up into the pyramid itself?
32:32One recent idea may explain this long-standing mystery.
32:36Many Egyptologists suspect that ramps were used.
32:41It's likely engineers used a large, single ramp leading to the pyramid.
32:46And the ancients knew it was crucial to get its angle right.
32:50Anything beyond six or seven degrees becomes very, very difficult to then push a large block uphill.
32:58But keeping the ramp shallow would force it to cover a huge distance.
33:02It would be miles long to get to the top of the pyramid.
33:07So it would take longer to build a ramp than it would take to build a pyramid.
33:11But that doesn't make any sense.
33:14Speculation continues as to exactly how the Egyptians built their giant monuments.
33:19Pyramids are so extraordinary that people have always struggled to believe that they could possibly have been built as long ago as they were.
33:30And their perfection has become a breeding ground for wild theories.
33:37With some suggesting that there's something else going on.
33:40People, when faced by the pyramids, look at this and think it can't possibly have been done without some force from outside.
33:49Did this ancient civilization have alien assistance?
33:53That couldn't possibly be true.
33:56The arguments are fabulously speculative.
33:58None of them plausible.
33:59None of them real.
34:00I feel quite offended on behalf of the ancient Egyptians that their abilities are called into question like this.
34:07Of course, the Egyptians built the pyramids.
34:10They did so brilliantly.
34:12There may be precious little evidence to support how the pyramids were built.
34:16But there's no doubt that these mighty tombs were constructed by skilled Egyptian craftsmen.
34:23Without any outside help.
34:27Certainly not from aliens.
34:28And the Egyptians' engineering brilliance didn't stop at the pyramids' limestone exterior.
34:37The Great Pyramid isn't a completely solid structure.
34:40There are chambers and pathways within it.
34:44A grand tomb for the king.
34:47With the king's chamber right at the pyramid's heart.
34:50Today, all that remains is Khufu's giant granite sarcophagus, along with two tiny shafts on the north and south walls.
35:01Originally, it was believed that these could be air shafts for the burial chamber, but that seems unlikely.
35:07Then, in 1964, astronomers made an extraordinary discovery.
35:14One shaft aligns precisely with Orion's belt, while the other lines up with the north star, as it would have appeared in ancient Egypt's night sky.
35:24Both shafts rise at constant angles, each running for more than 130 feet through the body of the pyramid.
35:32They are intended to provide a clear sight line from the burial chamber up to the stars.
35:39An engineering phenomenon, all to guide the king's spirit after death.
35:45There's a desire for the royal soul to emerge from the mummified body and ascend to not only the gods, but also to travel up into the night sky and join with the stars.
35:58Launch pads to the afterlife.
36:03But the pharaoh wouldn't ascend to the heavens empty-handed.
36:08Egyptian rulers were often buried with their most prized possessions to accompany them in death.
36:13Gold, silver, and bronze artefacts were loaded into their great tombs, while fine linens and artwork adorned the secret chambers.
36:24All the things that made yourself happy here and now, so you could carry it with you into the world beyond.
36:31But this wasn't simply about jewels or gold.
36:35Egypt's greatest treasure was the mummified body of the god-king, which must be protected at all cost.
36:42The burial chamber itself, it's quite incredible. It almost looks like a bank vault.
36:48Egyptian engineers are thought to have used a 3D-scale model of the burial chamber.
36:54A surprisingly modern technique for construction.
36:57If you were thinking about designing something like a pyramid today, we would be designing that digitally, so we'd have a 3D-digital model to understand what the space was like inside.
37:08No expense was spared in designing the king's burial chamber.
37:16Engineers devised a way to plug the passages with stone, sealing off the tomb.
37:23Securing the site where their king's journey into the afterlife would begin.
37:27In 2560 BC, after two decades of work, the Great Pyramid of Giza was completed.
37:42Khufu had created a symbol of his absolute rule.
37:47Towering 479 feet over the Egyptian desert.
37:51To see this, the biggest structure anyone had ever seen in all human history, I mean, it's hard to imagine what it must have been like.
38:03Armed with basic tools and clever engineering, the ancient Egyptians had created a structural marvel.
38:10It's staggering to think, for almost 4,000 years, the Great Pyramid of Giza was the tallest building on earth.
38:19An eternal testament to the power of their empire.
38:23This is a statement piece.
38:26The wealth, the might, the power, and how important this person is.
38:32Originally covered by a smooth, sloping layer of fine white limestone,
38:36the monument was once even more striking, gleaming in the sunlight.
38:44The last of the seven wonders of the ancient world to survive.
38:50It's one of the most well-studied buildings on earth.
38:54But there's still so much left to learn.
38:58In many ways, we've just scratched the surface.
39:00And the more rapidly modern technology develops, the more we're finding out about ancient Egypt.
39:08Often a discovery raises more questions than it answers.
39:14In 2017, scientists detected a previously unknown void within the structure.
39:21Techniques, including thermal imaging,
39:23helped identify a space roughly 98 feet long above the giant passageway leading to the king's chamber.
39:30It gets people really excited.
39:33And people think, there's another chamber.
39:36This could be where someone's buried and their goods are.
39:41But its true purpose remains a mystery.
39:47Despite archaeologists' best efforts,
39:50the Great Pyramid retains many of its deepest secrets.
39:53And it's just one of many pyramids yet to be fully explored.
40:02The ancient Egyptians went on to build more than 80 further pyramids across the country.
40:08But none surpassed the magnitude of Khufu's Great Pyramid.
40:12Over the centuries, the scale and precision of construction tailed off.
40:20They're not being built in the same way as those earlier pyramids.
40:24And what happens is these things don't stand the test of time.
40:27But why did Egypt's pyramid-building craze die out?
40:35Tomb Raiders were a massive problem for the Egyptians.
40:39People who were well aware of what was within those tubes.
40:43Of course, it doesn't take a genius to work out where that gold might be.
40:47You might as well just put a big cross.
40:49Eventually, the pharaohs were forced to change their approach to royal burials.
40:59A thousand years after the Great Pyramid Age,
41:02the pharaohs of the New Kingdom established a secret burial place on the Nile's west bank.
41:10The Valley of the Kings.
41:15More than 60 tombs were carved across this remote valley.
41:19The Valley of the Kings contains burials which are cut directly into the rock itself.
41:27Including the most famous Egyptian burial of them all.
41:32The Boy King Tutankhamun.
41:34Today, engineers have dug one structure deep underground.
41:54Not to protect a king, but to ensure the continued survival of nature itself.
41:59Deep in the bowels of an icy mountain on the island of Spitsbergen lies the Svalbard Global Seed Vault.
42:09A secure facility where more than a million seeds from the world's agricultural plants are kept.
42:15Constructed in 2008, the site was chosen for its position below permafrost and thick rock.
42:25Over 320 feet within the mountain.
42:28Where the seed samples will remain frozen, even if the power supply fails.
42:36It's a gigantic safety deposit box which holds the world's largest collection of agricultural biodiversity.
42:44The facility ensures that biodiverse plant life could be restored after a great natural disaster or global catastrophe.
42:53And as ancient Egypt's rulers continued to be buried away from prying eyes, the pyramids were soon forgotten.
43:08But elsewhere, their story was only just beginning.
43:14In a burst of creativity around the 8th century BC, one of Egypt's neighboring kingdoms began their own pyramid-building craze.
43:23Few people realize there are more than twice as many pyramids over the southern border in ancient Nubia, modern Sudan.
43:32But Sudan's pyramids would be radically different.
43:35Their angle of incline is far, far steeper than the Egyptian ones.
43:41And more often than not, they are considerably smaller.
43:44For visitors, these ancient structures are striking sights to behold.
43:49The last pyramids of ancient Africa.
43:54But on the far side of the world, other empires were rising.
44:05From around 1200 BC, advanced societies emerged in the Americas.
44:18The Olmec, Maya, and Aztecs flourished across the region, developing great civilizations up until the 16th century.
44:27And they had one thing in common.
44:36Pyramids.
44:37These civilizations began constructing the sky-high structures at a remarkable rate.
44:43We can literally say that thousands of pyramids dotted the Mesoamerican landscape.
44:53More pyramids than in the rest of the world combined.
44:59Topped with elaborate platforms, they became the glorious centerpieces to vast ancient cities.
45:05Believed to house their deities and serve as tombs for their dead kings.
45:11But was that the entire story?
45:15Do these mighty structures conceal a dark and bloody past?
45:24Once the most populous city in the Americas,
45:27Teotihuacan sprawled over an area larger than ancient Rome.
45:31Teotihuacan was a very large city, possibly having 100,000 inhabitants at the peak.
45:44The largest city anywhere in the Western Hemisphere.
45:48Yet little is known about the people who lived there.
45:53Teotihuacan was a major site.
45:56It was prominent until about 600, and then things began to decline.
46:05The city was suddenly abandoned.
46:07And it's still not clear why its people and their culture vanished overnight.
46:12We have several signs of destruction.
46:15Monuments were destroyed.
46:17The city was burned.
46:20Now, the pyramids and ruins are all that remain of this once majestic city.
46:26And they offer insight into the lives of the Teotihuacan people.
46:32But there have also been some disturbing discoveries.
46:37Beneath one of the city's largest structures, known as the Pyramid of the Moon,
46:43archaeologists were shocked by what they found.
46:46Underground chambers filled with animal and human remains, including human skulls.
46:52The ritual activity of the temples sometimes entailed the participation of human beings
47:02that were offered up ritually, individuals that were killed ritually.
47:09Some were captives of war.
47:12We know that they had their hands tied up.
47:17Large offerings, including human sacrifices, were made regularly in an attempt to appease the gods.
47:24Some even believed that it would prevent the apocalypse.
47:27Despite their bloody and brutal history, these monuments are marvels of the ancient world.
47:36Still standing centuries after their creators all but disappeared.
47:44Pyramids are among the most enduring icons of the ancient world.
47:48Even today, they feature heavily in architectural design.
47:57Modern architects still find that shape fascinating.
48:01Its perfection, its symmetry, the way that it connects us back to our history.
48:06And you see that now reflected in buildings around the world.
48:11The Luxor Las Vegas Pyramid is specifically modeled on Khufu's grand tomb,
48:17complete with its own sphinx and obelisk.
48:22And in Paris, the glass pyramid fronting the Louvre Museum is one of the city's most notable landmarks.
48:29That pyramid's shape is still something that we desire.
48:31I think there's something about the symmetry that we seem to have an affinity or a liking to.
48:36Pyramids are part of our common global culture.
48:40Even found on the U.S. dollar bill.
48:43A homage to Egyptian ancestry in updated form.
48:52Dating back more than 4,500 years,
48:57pyramids revolutionized construction in the ancient world.
49:01They consumed materials and labor on an unparalleled scale.
49:06Requiring engineering know-how never seen before.
49:10Today, they continue to inspire.
49:14And it doesn't look like these iconic structures will be going anywhere soon.
49:20The Pyramid.
49:22An ancient design so perfect,
49:25it has survived the ages.
49:26And it is seen hers.
49:42And it is possible.
49:46Thanks for joining us.