Joseph and Jourdan expected Wellington to advance along the great road from Valladolid to Burgos. Instead, the British general directed Hill and the right wing to advance just to the north of the road. Graham and the left wing were farther to the north. To Graham's left marched a Spanish corps led by Pedro Agustín Girón with 12,000 men. The French fell back behind the Pisuerga River and then to Burgos but, to their bewilderment only a handful of Spanish cavalry directly pursued them. Wellington's great flank march continued and the French abandoned Burgos on 13 June, blowing up the castle that had been the focus of the Siege of Burgos the previous autumn. Unsuspected by the French, the British commander was prepared to change his base from Lisbon to Santander on the Bay of Biscay.