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00:00 Why Are Cities Built on Top of Each Other?
01:11 What's Beneath the Basilica of San Clemente?
04:48 Artificial Hills (Tells) Explained
05:22 The Ancient City of Troy
06:08 Sinking Cities: Shanghai
07:00 Seattle's Underground City

--> YouTube-Generated Transcript <--
· Why Are Cities Built on Top of Each Other?
0:00 · This is what the Roman Forum looked like in 1864
0:04 · and this is what it looks like today.
0:06 · When archaeologists started digging here
0:08 · they uncovered an entire world of ruins deep underground
0:11 · that hadn't been seen for centuries.
0:14 · Over time, the city had risen by more than 10 meters
0:17 · and older buildings had been completely forgotten about.
0:20 · All over the world you'll find ruins
0:22 · that are slowly being left behind by the constant rise of the streets
0:27 · and modern cities that have been built on top of old ruins.
0:31 · The ancient city of Troy was rebuilt 10 times forming 10 distinct layers
0:36 · all built directly on top of each other.
0:39 · Even the city of Seattle has an entire network
0:41 · of mysterious, abandoned shops and houses
0:44 · buried beneath the modern streets.
0:46 · But why are cities built on top of each other?
0:49 · Is the street level actually rising?
0:51 · and why does history always end up buried deep underground?
0:55 · We modeled the entire thing
0:56 · to show you how civilizations build on top of each other.
1:00 · We'll also look at the crazy historical layers beneath Rome,
1:03 · these strange hills all over the Middle East,
1:06 · and the mysterious city purposefully buried beneath Seattle
1:09 · over 100 years ago.
· What's Beneath the Basilica of San Clemente?
1:11 · There is no single reason why cities are built on top of each other.
1:15 · After the great fire of Rome in the first century
1:18 · most of the city had to be rebuilt.
1:20 · But instead of clearing away the rubble
1:21 · it was quicker and easier to simply flatten it out and build on top.
1:25 · This meant that new buildings were about a meter higher than the street.
1:30 · And so, to match the new height
1:32 · the streets were raised and resurfaced
1:34 · using rocks from the surrounding debris.
1:36 · With every fire and natural disaster that occurred, this process would repeat itself
1:41 · raising the city and leaving old ruins buried underground.
1:44 · One of the clearest examples of this
1:46 · is the Basilica of San Clemente in Rome.
1:49 · The structure we see today is from the 12th century
1:52 · but it was built directly on top of an old church from the 4th century.
1:57 · That church was built directly on top of a mysterious old temple
2:01 · and that temple was built on top of an old house.
2:04 · And there are even older ruins beneath that.
2:07 · All in all, the valley in which San Clemente lies
2:10 · is now 18 meters higher than it was in the first century.
2:14 · Here's what happened.
2:15 · Back in 1st century Rome, before the Colosseum was built
2:19 · a Roman villa sat at the bottom of the valley.
2:22 · After being damaged in a fire
2:23 · it was converted into a temple by the Mithra people
2:26 · a mysterious cult which was gaining popularity throughout Rome.
2:30 · But by the end of the 4th century
2:32 · the temple was partially destroyed by the Christians.
2:35 · Looking to promote their religion, they decided to build a new basilica
2:39 · on top of the old temple.
2:41 · This basilica served the Christians for another 800 years
2:45 · But by the 12th century it fell into disrepair.
2:48 · After multiple fires and rebuilds around the basilica
2:52 · the street level had risen considerably
2:54 · and so instead of knocking it down a new basilica was built on top.
2:59 · This is the one we see today.
3:01 · Eventually, the ruins beneath the basilica were filled in
3:05 · and because no one kept track
3:06 · all knowledge of the previous layers was completely lost.
3:10 · But in the 1800s, an archaeologist started digging
3:13 · and unearthed the old basilica
3:15 · with a staircase leading down to the first century temple.
3:19 · Inside was a Mithra shrine
3:21 · and scrolled on the walls were paintings dedicated to the Mithra God
3:25 · [ad text redacted]
· Artificial Hills (Tells) Explained
4:48 · We've seen how Rome is built almost entirely on old ruins
4:52 · but one of the best examples of a layered city
4:55 · dates back to a time long before Rome ever existed.
4:59 · All over the Middle East
5:00 · you'll find these strange looking hills with mysteriously flat tops.
5:04 · These are known as tells.
5:06 · Tel as in Tel Aviv, which used to look like this.
5:10 · These are artificial hills formed by centuries of civilizations
5:15 · building on top of each other.
5:16 · Inside each tell is a world full of old ruins lost in time.
· The Ancient City of Troy
5:22 · Perhaps one of the most impressive of these is the ancient city of Troy
5:26 · which first began as a small settlement back in 3000 BC.
5:31 · The buildings were mostly made from mud bricks
5:34 · and when they were destroyed the material decomposed
5:37 · and covered the ruins and soil
5:39 · then a new settlement came along and built on top.
5:42 · Over the following millennia, eight more civilizations took over this mound
5:46 · going from the Persians to Alexander the Great, and eventually the Romans.
5:50 · Up until the year 500 AD
5:53 · when the nearby port dried up and the last civilization left the city.
5:58 · Eventually the buildings crumbled back into the hill
6:01 · and the soil took over, making Troy a complete mystery
6:04 · until it was discovered in the 1800s.
6:07 · In most cases humans are the main cause of layered cities
· Sinking Cities: Shanghai
6:11 · but there is something we haven't talked about yet.
6:13 · What happens when buildings and cities literally sink into the ground?
6:18 · Did you know that Shanghai is currently sinking
6:21 · by around 1 cm every year?
6:23 · In fact, most major cities across China are all sinking.
6:27 · For centuries, the only way to get fresh drinking water
6:30 · was to pump it out of the ground
6:32 · but by doing this, the pores that hold the water are emptied
6:35 · causing the ground to compress and sink.
6:38 · This is a problem all over the world, but the soil beneath Shanghai
6:41 · is particularly soft and with the sheer weight of all the skyscrapers sitting on top
6:46 · the city has shrunk around 3 meters in the last century.
6:50 · When cities sink too much they fall below sea level
6:53 · and end up completely lost.
6:55 · The only real solution to get above the water is to build on top.
6:59 · That is exactly what happened in Seattle.
· Seattle's Underground City
7:02 · Although Seattle is only 175 years old, it already has an entire network
7:07 · of streets and abandoned buildings hidden beneath the modern city.
7:11 · In 1889 a devastating fire ripped through the newly formed city
7:16 · and, just like Rome, almost everything had to be rebuilt.
7:20 · The mayor took this as an opportunity to drastically improve the city's design
7:25 · which already had huge problems with flooding.
7:27 · The idea was to raise the entire city
7:30 · and install drainage pipes underneath the streets
7:33 · allowing the water to naturally flow out to the sea.
7:36 · To pull this off
7:37 · 6 meter high stone walls were built on either side of the streets
7:41 · and roads were built on top.
7:44 · For a while, Seattle went through a weird phase
7:46 · with its buildings sat two stories below street level
7:49 · and people had to descend on ladders to get to shops and houses.
7:53 · Eventually the gaps were filled in and proper sidewalks were installed
7:56 · leaving behind a well preserved city right beneath Seattle's streets.
8:02 · And now, time for the Primal Space Giveaway.
8:04 · The winner of the previous giveaway is Jimmy! Congrats.
8:07 · In the next video we'll be giving away another $100 Amazon gift card to one lucky viewer.
8:13 · All you need to do is sign up at the link below
8:16 · like the video, and leave a comment saying what you think of these amazing underground ruins.
8:22 · Thank you very much for watching and I'll see you in the next video!

--> YouTube-Generated Transcript <--
	·	Why Are Cities Built on Top of Each Other?
0:00	·	This is what the Roman Forum looked like in 1864
0:04	·	and this is what it looks like today.
0:06	·	When archaeologists started digging here
0:08	·	they uncovered an entire world of ruins deep underground
0:11	·	that hadn't been seen for centuries.
0:14	·	Over time, the city had risen by more than 10 meters
0:17	·	and older buildings had been completely forgotten about.
0:20	·	All over the world you'll find ruins
0:22	·	that are slowly being left behind by the constant rise of the streets
0:27	·	and modern cities that have been built on top of old ruins.
0:31	·	The ancient city of Troy was rebuilt 10 times forming 10 distinct layers
0:36	·	all built directly on top of each other.
0:39	·	Even the city of Seattle has an entire network
0:41	·	of mysterious, abandoned shops and houses
0:44	·	buried beneath the modern streets.
0:46	·	But why are cities built on top of each other?
0:49	·	Is the street level actually rising?
0:51	·	and why does history always end up buried deep underground?
0:55	·	We modeled the entire thing
0:56	·	to show you how civilizations build on top of each other.
1:00	·	We'll also look at the crazy historical layers beneath Rome,
1:03	·	these strange hills all over the Middle East,
1:06	·	and the mysterious city purposefully buried beneath Seattle
1:09	·	over 100 years ago.
	·	What's Beneath the Basilica of San Clemente?
1:11	·	There is no single reason why cities are built on top of each other.
1:15	·	After the great fire of Rome in the first century
1:18	·	most of the city had to be rebuilt.
1:20	·	But instead of clearing away the rubble
1:21	·	it was quicker and easier to simply flatten it out and build on top.
1:25	·	This meant that new buildings were about a meter higher than the street.
1:30	·	And so, to match the new height
1:32	·	the streets were raised and resurfaced
1:34	·	using rocks from the surrounding debris.
1:36	·	With every fire and natural disaster that occurred, this process would repeat itself
1:41	·	raising the city and leaving old ruins buried underground.
1:44	·	One of the clearest examples of this
1:46	·	is the Basilica of San Clemente in Rome.
1:49	·	The structure we see today is from the 12th century
1:52	·	but it was built directly on top of an old church from the 4th century.
1:57	·	That church was built directly on top of a mysterious old temple
2:01	·	and that temple was built on top of an old house.
2:04	·	And there are even older ruins beneath that.
2:07	·	All in all, the valley in which San Clemente lies
2:10	·	is now 18 meters higher than it was in the first century.
2:14	·	Here's what happened.
2:15	·	Back in 1st century Rome, before the Colosseum was built
2:19	·	a Roman villa sat at the bottom of the valley.
2:22	·	After being damaged in a fire
2:23	·	it was converted into a temple by the Mithra people
2:26	·	a mysterious cult which was gaining popularity throughout Rome.
2:30	·	But by the end of the 4th century
2:32	·	the temple was partially destroyed by the Christians.
2:35	·	Looking to promote their religion, they decided to build a new basilica
2:39	·	on top of the old temple.
2:41	·	This basilica served the Christians for another 800 years
2:45	·	But by the 12th century it fell into disrepair.
2:48	·	After multiple fires and rebuilds around the basilica
2:52	·	the street level had risen considerably
2:54	·	and so instead of knocking it down a new basilica was built on top.
2:59	·	This is the one we see today.
3:01	·	Eventually, the ruins beneath the basilica were filled in
3:05	·	and because no one kept track
3:06	·	all knowledge of the previous layers was completely lost.
3:10	·	But in the 1800s, an archaeologist started digging
3:13	·	and unearthed the old basilica
3:15	·	with a staircase leading down to the first century temple.
3:19	·	Inside was a Mithra shrine
3:21	·	and scrolled on the walls were paintings dedicated to the Mithra God
3:25	·	[ad text redacted]
	·	Artificial Hills (Tells) Explained
4:48	·	We've seen how Rome is built almost entirely on old ruins
4:52	·	but one of the best examples of a layered city
4:55	·	dates back to a time long before Rome ever existed.
4:59	·	All over the Middle East
5:00	·	you'll find these strange looking hills with mysteriously flat tops.
5:04	·	These are known as tells.
5:06	·	Tel as in Tel Aviv, which used to look like this.
5:10	·	These are artificial hills formed by centuries of civilizations
5:15	·	building on top of each other.
5:16	·	Inside each tell is a world full of old ruins lost in time.
	·	The Ancient City of Troy
5:22	·	Perhaps one of the most impressive of these is the ancient city of Troy
5:26	·	which first began as a small settlement back in 3000 BC.
5:31	·	The buildings were mostly made from mud bricks
5:34	·	and when they were destroyed the material decomposed
5:37	·	and covered the ruins and soil
5:39	·	then a new settlement came along and built on top.
5:42	·	Over the following millennia, eight more civilizations took over this mound
5:46	·	going from the Persians to Alexander the Great, and eventually the Romans.
5:50	·	Up until the year 500 AD
5:53	·	when the nearby port dried up and the last civilization left the city.
5:58	·	Eventually the buildings crumbled back into the hill
6:01	·	and the soil took over, making Troy a complete mystery
6:04	·	until it was discovered in the 1800s.
6:07	·	In most cases humans are the main cause of layered cities
	·	Sinking Cities: Shanghai
6:11	·	but there is something we haven't talked about yet.
6:13	·	What happens when buildings and cities literally sink into the ground?
6:18	·	Did you know that Shanghai is currently sinking
6:21	·	by around 1 cm every year?
6:23	·	In fact, most major cities across China are all sinking.
6:27	·	For centuries, the only way to get fresh drinking water
6:30	·	was to pump it out of the ground
6:32	·	but by doing this, the pores that hold the water are emptied
6:35	·	causing the ground to compress and sink.
6:38	·	This is a problem all over the world, but the soil beneath Shanghai
6:41	·	is particularly soft and with the sheer weight of all the skyscrapers sitting on top
6:46	·	the city has shrunk around 3 meters in the last century.
6:50	·	When cities sink too much they fall below sea level
6:53	·	and end up completely lost.
6:55	·	The only real solution to get above the water is to build on top.
6:59	·	That is exactly what happened in Seattle.
	·	Seattle's Underground City
7:02	·	Although Seattle is only 175 years old, it already has an entire network
7:07	·	of streets and abandoned buildings hidden beneath the modern city.
7:11	·	In 1889 a devastating fire ripped through the newly formed city
7:16	·	and, just like Rome, almost everything had to be rebuilt.
7:20	·	The mayor took this as an opportunity to drastically improve the city's design
7:25	·	which already had huge problems with flooding.
7:27	·	The idea was to raise the entire city
7:30	·	and install drainage pipes underneath the streets
7:33	·	allowing the water to naturally flow out to the sea.
7:36	·	To pull this off
7:37	·	6 meter high stone walls were built on either side of the streets
7:41	·	and roads were built on top.
7:44	·	For a while, Seattle went through a weird phase
7:46	·	with its buildings sat two stories below street level
7:49	·	and people had to descend on ladders to get to shops and houses.
7:53	·	Eventually the gaps were filled in and proper sidewalks were installed
7:56	·	leaving behind a well preserved city right beneath Seattle's streets.
8:02	·	And now, time for the Primal Space Giveaway.
8:04	·	The winner of the previous giveaway is Jimmy! Congrats.
8:07	·	In the next video we'll be giving away another $100 Amazon gift card to one lucky viewer.
8:13	·	All you need to do is sign up at the link below
8:16	·	like the video, and leave a comment saying what you think of these amazing underground ruins.
8:22	·	Thank you very much for watching and I'll see you in the next video!