Madrid now gave itself up to gaiety--balls, bull-fights, illuminations, and fêtes of every description, and a week later the 51st marched to the Escorial, where it was quartered until the 1st September. On that day Wellington, leaving two divisions under General Hill at Madrid, took the remainder of his army with him and marched north, for the purpose of driving back the enemy from the Douro to Burgos. "Our march," says Ensign Mainwaring of the 51st, "though rapid, was by no means disagreeable; for traversing a rich wine-country, our route lay through vast plains covered with vineyards, and at this season, autumn, just before the vintage, the vines were laden with clusters of ripe grapes, tempting to the appetite and beautiful to the eye. In this manner we travelled on, without anything occurring worthy of note till we came within sight of the castle of Burgos, and we began to anticipate, not with much pleasure, all the inglorious toils and arduous and fatiguing business of a siege--the most disagreeable military duty a soldier has on service, digging and delving in dust and dirt like ploughmen, to shelter ourselves, ere morning's dawn, from shot and shell whizzing about our ears at each moment, killing or mutilating our next neighbour. No excitement, as in a general action, by the immediate prospect of getting at the foe, your only hope that you may get through your twenty-four hours in the trenches unscathed, back to your bivouac, to eat, drink, and sleep till your turn in the batteries comes round again, varied by the storm of an outwork or a sortie of the enemy, to either of which occurrences the soldier looks forward as something to enliven and break in upon the routine of his daily labours." Clausel had withdrawn slowly from the Douro as Wellington advanced, and on the 18th September passed through Burgos, leaving a garrison of eighteen hundred men in the castle. To invest and reduce this Wellington set to work immediately, twelve thousand men being detailed for the siege and twenty thousand for the covering force. So strong, however, was the castle, and so determined the garrison, that after an investment of thirty-three days, during which time five separate assaults were delivered and repulsed, and several desperate sallies of the garrison were met and beaten back, Wellington was obliged to abandon the enterprise and raise the siege, when he learned, in the middle of October, that Clausel, having received a reinforcement of twelve thousand fresh troops from France, was marching down upon him with some forty-four thousand men. During these operations the 51st, with the remainder of the 7th Division, formed part of the covering army, watching the country between Burgos and Vittoria, and spending some days near the village of Monasterio, but never called upon to do more than check reconnaissances pushed out by the enemy.