Now known as Konye-Urgench or Old Urgench, this ruined ancient city exists alongside modern Urgench, founded over two millenia later. Old Urgench was likely settled by the 5th century BC, and is recorded as having been conquered by Arabs in the 8th century AD. Over the following centuries, Urgench expanded to become one of the major cities of central Asia. As Merv contributed translators to other cities, so Urgench was said to contribute architects and builders, who are known to have participated in the development of a considerable number of structures in nearby Samarkand and Bukhara. Like these cities, Urgench was sacked and largely destroyed by the Mongols in the 13th century. In the 15th century, the Amu Darya River changed its course, leaving the city without its primary source of water and cutting off access to a key trading artery. Urgench was supplanted by Khiva as the region's chief city, and was abandoned by its residents by the 16th century. The ruins of Konye-Urgench are now preserved as a UNESCO World Heritage site.