Alodia was in the savannah belt, giving it an economic advantage over its northern neighbor Makuria. According to al-Aswani the "provisions of the country of Alwa and their king" came from Kersa, which has been identified with the Gezira. North of the confluence of the two Niles agriculture was limited to farms along the river watered by devices like the shadoof or the more sophisticated sakia. In contrast, the farmers of the Gezira profited from sufficient rainfall to make rainfall cultivation the economic mainstay.