Unlike many other regions of the world, Central Asia lacks the distinct topographical features necessary to delineate boundaries. There are several broad geographical zones in Central Asia nonetheless. Perhaps the most well-known topographic area in Central Asia is the great Eurasian Steppe, a latitudinal belt of grassland that stretches from Eastern Europe through Mongolia. It was there that nomadic horse cultures flourished. Located to the south of the steppe was the core of Central Asia, an area known as Transoxiana. This is a dry region that lies beyond the Oxus River, known today as the Amu Darya. In Transoxiana trade settlements and irrigated agriculture developed along the Amu Darya and Syr Darya watersheds. Finally, located to the far south, lies the mountainous area of Khorasan, the cultural capital of Persia prior to the appearance of the Mongols.