visible from a day's journey away. In 1221, the city opened its gates to an invading Mongol horde, resulting in massive devastation. Historical accounts contend that the entire population (including refugees) were killed; Tolui Khan is reputed to have slaughtered 700,000 people. Though partly rebuilt after the Mongol destruction, the city never regained its former prosperity. Between 1788 and 1789, the city was razed for the last time, and its population deported. By the 1800s, under pressure from the Russians, Merv was completely deserted. Today the site is preserved by the Government of Turkmenistan as the State Historical and Cultural Park "Ancient Merv" established in 1987 and regulated by Turkmenistan's legislation. It is the oldest and most perfectly preserved of the oasis cities along the historical Silk Road in Central Asia. A few buildings and structures still stand today, especially those constructed in the last two millennia. UNESCO has listed the site of ancient Merv as a World Heritage Site. History Merv has prehistoric roots: archaeological surveys have revealed many traces of village life as far back as the 3rd millennium BC and have associated the area culturally with the Bactria-Margiana Archaeological Complex. The geography of the Zend-Avesta (commentaries on the Avesta) mentions Merv (under the name of Mouru) along with Balkh. In Zoroastrianism, the god Ahura Mazda created Mouru as one of sixteen perfect lands. Under the Achaemenid Empire (c. 550–330 BC), the historical record mentions Merv as a place of some importance: under the name of Margu, it occurs as part of one satrapy in the Behistun inscriptions (ca. 515 BC) of the Persian monarch Darius the Great. The first city of Merv was founded in the 6th century BC as part of the Achaemenid expansion into the region of Cyrus the Great (559–530 BC), but later strata deeply cover the Achaemenid levels at the site. Hellenistic era Alexander the Great's visit to Merv is merely legendary, but the city was named Alexandria (Ἀλεξάνδρεια) after him for a time. After his death in 323 BC, it became the capital of the Province of Margiana of the Seleucid, Greco-Bactrian (256–125 BC), Parthian, and Sassanid states. The Seleucid ruler, Antiochus Soter (reigned 281–261 BC), renamed it to Antiochia Margiana; he rebuilt and expanded the city at the site presently known as Gyaur Gala fortress. Isidore of Charax wrote Antiochia was called the "unwatered" (Ἄνυδρος). Parthian era After the fall of