A major change came in July 1346, when Edward staged a major offensive, sailing for Normandy with a force of 15,000 men. His army sacked the city of Caen, and marched across northern France, to meet up with English forces in Flanders. It was not Edward's initial intention to engage the French army, but at Crécy, just north of the Somme, he found favourable terrain and decided to fight a pursuing army led by PhilipVI. On 26 August, the English army defeated a far larger French army in the Battle of Crécy. Shortly after this, on 17 October, an English army defeated and captured King DavidII of Scotland at the Battle of Neville's Cross. With his northern borders secured, Edward felt free to continue his major offensive against France, laying siege to the town of Calais. The operation was the greatest English venture of the Hundred Years' War, involving an army of 35,000 men. The siege started on 4September 1346, and lasted until the town surrendered on 3August 1347.