11He Cheng & Shi Cheng
Two ancient Chinese cities were drowned when the valley was flooded for a new hydroelectric power station. He Cheng and Shi Cheng remained forgotten for 40 years until 2001. Shi Cheng was built more than 1300 years ago in 621 AD. It was once the center of politics, economics and culture. He Cheng is even older: established in 208 AD as a business hub.
12Lost City of Zakynthos
When snorkelers discovered what appeared to be ancient stonework off the coast of the Greek island of Zakynthos in 2013, archaeologists sent to the site thought the odd rocks might be the ruins of an ancient city. Turns out, the so-called Lost City of Zakynthos was not built by humans, but by methane-eating microbes.
In 1963, a man tore down a wall in his house and noticed an enormous and complex tunnel system behind it. He had rediscovered the ancient underground city Derinkuyu in Turkey. The city had 9 levels, used to house 20,000 people and had amenities such as stables, wineries, schools, and chapels. It was built between 1200 and 800 B.C.
The ancient city of Gobekli Tepe in Turkey built in 10,000 B.C., is twice as old as Stonehenge, and completely disrupts our ideas of human development and agriculture. Carvings on a stone located at the site depict a comet strike that researchers have theorized caused a worldwide cataclysmic event, which in turn brought on a 1000 year ice age known as the Younger Dryas. It predates the invention of known tools, cities/communities, and the written word. The oldest known sphinx was found in Gobekli Tepe, Turkey and it was dated to 9,500 BC.
The Aztec capital Tenochtitlán was the largest city in the Americas with over 200,000 people. It was built on a man-made island in the middle of a lake - connected to the shore by 3 causeways. It contained huge pyramids, floating gardens, aqueducts, and canals. It was destroyed by the Spanish in 1521.
The Greek city of Helike sank in an earthquake in 373 B.C., and all of the inhabitants died. Over time, it was silted over and was thought to be legendary until it was rediscovered in 2001.
The Ancient city of Uruk at 2900 B.C. had 50,000 - 80,000 residents living in its 6 square km of walled area, making it the largest city in the world at the time.
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Almost every home in the ancient city of Mohenjo-Daro from over 4000 years ago was equipped with a private bathing area with drains to take the dirty water out into a larger drain that emptied into a sewage drain.
19Tikal and Calakmul
The city-states of the ancient Maya were dominated by two cities, Tikal and Calakmul, who fought a series of conflicts through proxy states. Some experts have compared these conflicts to US-Soviet fighting by proxy during the Cold War.
The largest brick arch in the world, the 121-foot (37 m) tall Taq-i Kisra, is nearly 1,500 years old and it is the only surviving structure from the ancient city of Ctesiphon.