Merv is another ancient city in Turkmenistan that is listed in the UNSECO World Heritage List. The city is mentioned in the Zoroastrian Avesta (around 500 BC) as an important urban center. It is said that in 12th century Merv was the most populated city on the planet.
The city was conquered consequently by Arabs, Turks, Mongols, and Uzbeks. Now, there are several separate walled parts in ancient Merv, each built at different time and abandoned by people due to different reasons.