Unlike many other regions of the world, Central Asia lacks the distinct topographical features necessary to delineate boundaries. However, there are several broad geographical zones. The great Eurasian Steppe is 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. Beyond the Oxus River is a dry region referred to as Amu Darya today. 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.