There are some cities that were very famous in the past but have since been destroyed or abandoned.
Angkor was once the largest city in the world and more than a million people lived there. The city had an area of more than 78sq km and was surrounded by a water-filled moat. It was abandoned in about AD 1100. French naturalist Henri Mouhot was the first westerner to discover the city, in 1861.
Some people believe that there was a city and island of Atlantis, perhaps in the Mediterranean, that was destroyed by an earthquake and flooding almost 12,000 year ago. No one knows exactly where it was or even whether it really existed.
Chichen Itza was once the centre of the Mayan empire. It was built in about AD 400 and had many buildings used in Mayan rituals. The city was abandoned in AD 1200.
This Native American Indian city was built on a cliff side, but was abandoned during a long drought in the late 13th century. It lay unknown until 18 December 1888, when Richard Wetherill, a local farmer, spotted it while looking for stray cattle.
The fortified Inca city on top of a mountain was stumbled on in 1911 by American explorer Hiram Bingham. He was searching for Vilcamamba, another lost Inca city.
The entire city was buried by volcanic ash when Mount Vesuvius erupted in AD 79. Nearby Herculaneum was buried at the same time. Excavations began in 1748, and many treasures have been uncovered, including beautifully preserved murals (wall paintings). Plaster casts have been made of the bodies of inhabitants who were buried beneath the debris.
Troy was once thought to have existed only in legands, but its site was discovered in the 1870s.
Ur was once one of the the greatest cities in the world, but was abandoned in the 4th century BC. Its magnificent royal tombs and other sites were excavated by archeologists in 1922-34 and many treasures discovered.