On the 23rd of June, the TWELFTH Light Dragoons were detached, with other forces under Lieut.-General Sir Thomas Graham, by the pass of Adrian to the district of Guipuscoa, in the province of Biscay, and in the evening the head of the column, having crossed the Mutiol mountain, descended upon Segura. The TWELFTH passed the night in the mountain, resumed the march on the following day, and arrived in the evening in the neighbourhood of _Villa Franca_, at the moment when the rear-guard of General Foy's division, which was escorting a valuable convoy towards France, was entering the town. The French took up a strong position, some sharp fighting occurred, and eventually General Foy fell back to _Tolosa_, from whence he was driven with the loss of four hundred men killed and wounded; but the convoy entered France in safety. In the beginning of July, _St. Sebastian_ was besieged, and the TWELFTH Light Dragoons were employed in covering the siege of that important fortress. Towards the end of July, when Marshal Soult advanced with a powerful army to drive the allies from the Pyrenees and relieve the invested fortresses, the siege of St. Sebastian was turned into a blockade, and Major-General Anson's brigade of cavalry was employed in keeping up the communication through the mountains, between the left and centre of the allied army. The communication was interrupted on the 27th and 28th of July; but was renewed on the 29th, and after much hard fighting in the mountains, the French were driven back with loss. The siege of St. Sebastian was then renewed, and the TWELFTH Light Dragoons took post at Usurbil, from whence a squadron was subsequently detached to Renterio to furnish the out-posts in that direction. St. Sebastian was taken by storm on the 31st of August, and on the 9th of September the citadel surrendered. About this period Major-General Vandeleur was appointed to the command of the brigade of which the TWELFTH Light Dragoons formed part. After the fall of St. Sebastian, the troops which had been employed in the siege advanced to the frontiers, and on the 7th of October the passage of the _Bidassoa_ was forced, and the army entered France. Unprincipled aggression was thus overtaken by retributive justice, and the kingdom which had sent its legions to other countries to ravage and devastate, became the theatre of war. After the passage of the river, the TWELFTH Light Dragoons bivouacked on the great road, with posts at Urogne.