Merv 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's origins are prehistoric: archaeological surveys have revealed many traces of village life as far back as the 3rd millennium BC and that the city was culturally part of the Bactria-Margiana Archaeological Complex. Under the name of Mouru, Merv is mentioned with Balkh in the geography of the Zend-Avesta (commentaries on the Avesta). Mouru was among the sixteen perfect lands created by Ahura Mazda.
Under the Achaemenid dynasty Merv is mentioned as being a place of some importance: under the name of Margu it occurs as part of one of the satrapies in the Behistun inscriptions (ca. 515 BC) of the Persian monarch Darius Hystaspis. The first city of Merv was founded in the 6th century BC as part of the expansion into the region by the Achaemenid Empire of Cyrus the Great (559–530 BC), but the Achaemenid levels are deeply covered by later strata at the site.
Alexander the Great's visit to Merv is merely legendary, but the city was named Alexandria for a time. After Alexander's death, Merv became the capital of the Province of Margiana of the Seleucid, Bactrian, Parthian, and Sassanid states. Merv was renamed Antiochia Margiana by the Seleucid ruler Antiochus Soter, who rebuilt and expanded the city at the site presently known as Gyaur Gala (Turkish Gayur Kala) (Fortress). It was ruled in succession by Bactria, Parthia, and the Kushans after the fall of the Seleucid dynasty. It was a major city of Buddhism learning with Buddhist monastery temples for many centuries until its Islamicization. At the site of Gyaur Kala and Bairam Ali Buddhism was followed and practised often at the Buddhist stupa.
After the Sassanid Ardashir I (220–240 AD) took Merv, the study of numismatics picks up the thread: a long unbroken direct Sassanian rule of almost four centuries is documented from the unbroken series of coins originally minted at Merv. During this period Merv was home to practitioners of various religions beside the official Sassanid Zoroastrianism, including Buddhists, Manichaeans, and Christians of the Church of the East. Between the 6th (553) and 11th centuries AD, Merv was the seat of an East Syrian metropolitan province. Sassanid rule was briefly interrupted by the Hephthalite occupation from the end of the 5th century to 565 a.d.