Battle of the Green Fork

With the Riverlands plundered and Riverrun under siege by Jaime Lannister, Lord Tywin leaves Harrenhal and marches for the Green Fork of the Trident, the only crossing north besides the Twins, hoping to block the host coming down from Winterfell there.

What Tywin does not know is that Catelyn Tully has already talked Lord Walder Frey out of his neutrality, opening the river crossing to the northmen. With that door open, Robb splits his army in two: the infantry and part of the horse, under Roose Bolton, march down the Kingsroad toward Ruby Ford as bait, while Robb himself keeps most of the cavalry and rides another way.

Bolton marches by night hoping to catch the Lannister camp off guard, but at dawn he finds an army already drawn up. Tywin has arranged his men in several bodies: the vanguard of riders under Gregor Clegane, the center of heavy foot under Kevan Lannister, the right of cavalry under Addam Marbrand, the left made up of the mountain clansmen under Tyrion Lannister, and a reserve Tywin leads himself.

The northmen charge first, horns sounding, and a storm of Lannister arrows answers before the lines meet. The half-circle of Stark spearmen on the right flank holds Clegane's first push under another rain of shafts, but slowly gives ground to the horsemen; by the end the fighting has shifted several hundred yards, and the northmen fall back toward the hills as a final charge breaks what is left of their line.

Tyrion, leading mounted archers, sellswords and untrained recruits, throws himself into the close fighting: he rides down one man, kills another, and forces a knight trying to capture him to yield. His father later explains that the undisciplined mix on the left was meant as bait, to draw the northern commanders into attacking there while Kevan closed the center and Tywin came up from behind to pin them against the river. Roose Bolton does not take the bait; once he sees the battle is lost, he orders the retreat.

Tywin holds the field, but the real point of the northern move is won elsewhere: while he fights by the Green Fork, Robb falls on Jaime Lannister's undefended camp at the Battle of the Whispering Wood. Bolton's diversion has bought him the time he needed.

The cost to the northmen is heavy. Of those who marched with Bolton, only he, a handful of captains and about two thirds of the men make it back to the Twins. Lord Halys Hornwood, lord of Hornwood, dies on the field, along with Ser Pate of the Blue Fork; Lord Medger Cerwyn is taken prisoner and dies soon after of his wounds. Among those captured are Harrion Karstark, Wylis Manderly, Jared Frey, Hosteen Frey, Danwell Frey and Ronel Rivers.

Once he finally learns where the other northern army is, Tywin forces a fast march toward Riverrun, leaving behind the wounded who cannot keep pace. He arrives too late: Robb has already been camped before the castle for days by the time his father reaches the walls.