The Yarmuk itself is the most commanding river of all the east-Jordan land.
The Jaulan slopes southward to the Yarmuk and westward to the Jordan.
South of the Yarmuk the black basalt of the Jaulan yields to the light limestone of the west-Jordan.
In their upper courses they flow on the surface of the ground, but soon sink into deep gorges which lead to the Yarmuk.
The latter region probably lay to the north and east of the upper waters of the Yarmuk.
The heart of the east-Jordan land is the wide, level plain watered by the tributaries of the Yarmuk River.
From here Judas evidently marched northward across the Yarmuk to the town of Casphor.