After the death of Edward I, his ineffectual son, Edward II, abandoned the war against Scotland. During the following seven years, Robert I the Bruce, united Scotland under his rule and forced the English out of all the castles north of the Tweed River except for Berwick and Stirling.  When these tow remaining English castles came under siege, Edward II marched north with a strong army of 15,000 men, including 2000 armored knights.

To meet this force, Robert I deployed thousands of spearmen on a small rise overlooking Bannock burn, a tributary of the Forth River.  His peasant infantry was grossly outnumbered 3-1. He anchored his left flank in a patch of dense woods and his right on a bend in the stream.  As a reserve, Robert I held back a force of 500 mounted knights.

While the large English army was still splashing across the Bannock preparing to attack up the slope against the Scottish lines, the Bruce seized the opportunity to attack on a 2000 yard front with four circles of spearmen from the right swinging to the left flank. The two sides became locked together in a deadly struggle.  Edward II sent his archers around the Scottish left flank, but Bruce's mounted knights drove them back into the great mass of English troops.  Here the spears of the Scots created havoc among the cramped men and horses of the English. Finally the English front broke and began to fall back while the Scots pressed their advantage and turned the retreat in to a route. Edward II barely managed to escape, but the vast majority of his men, bogged down in the marshy ground along the bannock, fell victim to Scottish spears or drowned trying to escape. This was the greatest loss ever suffered by English Knighthood in a single day, with some 4,000 Scots being killed.