The Battle of the Green Fork was fought upon the eastern bank of that branch of the Trident, below the Twins, and though Lord Tywin Lannister carried the field it did not bring him the victory he supposed he had won. Robb Stark, dividing his host at the crossing of the Twins, had given the greater part of his foot to Roose Bolton, Lord of the Dreadfort, with orders to march down the kingsroad and give Lord Tywin battle, or at least the seeming of it. The purpose was not to beat the Lannister host but to hold its attention and pin it in place, while Robb himself led all his horse west against Ser Jaime at Riverrun. The men Bolton commanded were in large part the poorest and least of the northern levies, and it is said, by those inclined to think ill of the Lord of the Dreadfort, that he was well content to spend them.
Lord Tywin drew up his host in the night and gave battle at dawn. He set his least reliable troops, the wild hill clansmen of the Vale, upon his left under the command of his son Tyrion Lannister, thinking to blood them where their breaking would do least harm; against all expectation the imp survived the crush of the vanguard. The battle itself was a grinding affair of foot against foot, and in time the greater discipline and numbers of the Lannister host told. The northern line gave way, and Bolton drew off his survivors in good order back across the Green Fork, burning the bridges behind him so that Tywin could not pursue.
Lord Tywin held the field and counted himself the victor, and by the plain reckoning of arms he was. Yet he had beaten only a part of Robb Stark's strength, and the wrong part, while the young wolf and all his cavalry had slipped away unseen into the west. Within days word reached the Lannister camp that Ser Jaime had been taken and his army destroyed in the Whispering Wood, and Tywin understood too late that his hard-won battle on the Green Fork had been no more than the shadow that hid the true blow. He broke off and marched south to guard against a stroke at the capital, and the initiative in the riverlands passed for a season to House Stark.