Merv is a set of walled cities side by side, built over 2,000 years as the settlement moved across the oasis: Erk Kala, Gyaur Kala, Sultan Kala and others.
Under the Seljuk Sultan Sanjar in the 12th century Merv was a city of libraries, observatories and gardens. His mausoleum, finished around 1157, still stands with its great double dome.
In 1221 the Mongols under Tolui, son of Genghis Khan, destroyed the city and killed most of its people. Merv never recovered.
