Leading a host of 18,000 troops from the North, Robb Stark means to confront the Lannister armies in the Riverlands and relieve the forces loyal to his grandfather which have been under attack for some time. Lord Tywin Lannister has split his forces into two armies, each numbering approximately 30,000 men. One force, under the command of Jaime Lannister, lays siege to Riverrun, the seat of House Tully. The other, under Tywin's direct command, marches north, along the west bank of the Green Fork of the River Trident, to prevent the Starks from lifting the siege, and sends scouts to reconnoiter the Stark position.