The Solo River played a major role in the development of these settlements. It acted as source of water and fertile soil, and a means of transportation. A set of copper plates of the Ferry Charter (1358 C.E.) lists over twenty ferry crossing on the lower stretch of the Solo River, downstream from Bojonegoro. Inland settlements would trade agricultural products via trading centres in the coastal cities, like neighbouring Tuban, for spices from Spice Islands, ceramics from China and other commodities.