Ancient Merv State Historical and Cultural Park is located in the southeastern part of Turkmenistan, north of the city of Bayramaly and northeast of the city of Mary. The first human settlements in this place were recorded in the third millennium BC, and Merv saw the last inhabitants in the 18th century AD. The city is located on the former Silk Road, which much contributed to its growth. In the 12th and 13th centuries, it was among the three largest cities in the world with about half a million inhabitants. When the city authorities opened the city gates to the Mongol hordes in 1221, the result was the death of about a million people, residents, and refugees who sought refuge and the destruction of the city. Though Merv was rebuilt after that, the level of prosperity it had never regained. UNESCO placed Merv on the World Heritage Sites list in 1999.