Merv (Persian: Marv), formerly Achaemenid Satrapy of Margiana, and later Alexandria and Antiochia in Margiana, was a major oasis-city in Central Asia, on the historical Silk Road, located near today's Mary in Turkmenistan. Several cities have existed on this site, which is significant for the interchange of culture and politics at a site of major strategic value. It is claimed that Merv was briefly the largest city in the world in the 12th century. The site of ancient Merv has been listed by UNESCO as a World Heritage Site.
Merv consists of a few discrete walled cities very near to each other, each of which was constructed on uninhabited land by builders of different eras, used, and then abandoned and never rebuilt. Four walled cities correspond to the chief periods of Merv's importance: the oldest, Erkgala, corresponds to Achaemenid Merv, and is the smallest of the three. Gawurgala, which surrounds Erkgala, comprises the Hellenistic and Sassanian metropolis and also served as an industrial suburb to the Abbasid/Seljuk city, Soltangala – by far the largest of the three. The smaller Timurid city was founded a short distance to the south and is now called Abdyllahangala. Various other ancient buildings are scattered between and around these four cities; all of the sites are preserved in the “Ancient Merv Archaeological Park” just north of the modern village of Bayramaly and thirty kilometers east of the large Soviet-built city of Mary