After the various subtractions of strength, Joseph had only 33,000 infantry, 9,000 cavalry, and 100 guns to face Wellington. Napoleon assured his brother Joseph that the British general was too cautious to take advantage of the situation, and in any case could only deploy 30,000 British and 20,000 Portuguese soldiers. In fact, Wellington was on the march with 52,000 British, 28,000 Portuguese, and 25,000 Spanish troops. The three-division right wing under
Rowland Hill was ordered to advance northeast to
Salamanca while the six-division left wing led by
Thomas Graham crossed to the north bank of the
Douro River inside Portugal. Joseph and Jourdan posted Gazan's Army of the South and d'Erlon's Army of the Center to cover
Valladolid and
Segovia, while Reille with the remaining 17,000 troops from the Army of Portugal was sent to the north to help suppress guerillas. At this time, Clausel's 20,000 soldiers were located near
Pamplona, far to the east. Hill's wing seized Salamanca on 26 May 1813, chasing
Eugene-Casimir Villatte's French troops out of the city and capturing 200 French soldiers. Meanwhile, Graham's soldiers forded the flooding
Esla River at
Almendra on 31 May, losing some men to drowning and much equipment.
Augustin Darricau, whose division held
Zamora, had sent a cavalry reconnaissance to the west on 20 May that reported no enemy activity. The French horsemen just missed Graham, who crossed the Douro soon afterward. Finally alerted that 64,000 men were bearing down on Zamora from the northwest, Darricau bolted to the east, leaving Graham to occupy the town on the morning of 2 June. The same day,
Colquhoun Grant's cavalry brigade consisting of the
10th,
15th, and
18th Hussar Regiments defeated a French cavalry force at
Morales de Toro. The French mounted troops comprised the 16th and 21st
Dragoon Regiments under
Pierre Benoît Soult and their horses were in very bad condition. The 16th was virtually destroyed, with two officers and 308 troopers being made prisoners; of these 100 were wounded. British casualties in the clash were only 16 killed and wounded. On 3 June, Hill's wing joined Graham on the north bank of the Douro at
Toro. At this time, Wellington had 90,000 troops concentrated while the French could only count 51,000 men. Alarmed at the odds against them, Joseph and Jourdan sent a frantic message to Clausel asking for help and withdrew toward
Burgos. 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. During the French retreat, Reille turned up with three divisions of the Army of Portugal, adding 15,000 men to Joseph's army. Clausel's 25,000 troops were at large but Joseph had no idea where they were. For his part, Clausel never received any messages from the king until 15 June, at which time he gathered four divisions and set out to join the main army. Joseph massed his army behind the
Ebro River, believing that it would be impossible for Wellington's army to outflank the line on the north. On 15 June, Hill's wing crossed the Ebro at Puente Arenas and Graham's wing crossed at San Martin de Lines. From the 13th until a cavalry encounter on 17 June, the French lost all contact with their adversaries. ==Osma==