Marshal Mortier, with the fifth corps, was also directed to assist in the siege, and he was in march to join Moncey, when his progress also was arrested by sir John Moore’s advance towards Burgos. But the utmost scope of that general’s operation being soon determined by Napoleon’s counter-movement, Mortier resumed his march to reinforce Moncey, and, on the 20th of December, their united corps, forming an army of thirty-five thousand men of all arms, advanced against Zaragoza. At this time, however, confidence had been restored in that town, and all the preparations necessary for a vigorous defence were completed. The nature of the plain in which Zaragoza is situated, the course of the rivers, the peculiar construction of the houses, and the multitude of convents have been already described, but the difficulties to be encountered by the French troops were no longer the same as in the first siege. At that time but little assistance had been derived from science, but now, instructed by experience and inspired as it were by the greatness of their resolution, neither the rules of art nor the resources of genius were neglected by the defenders. Zaragoza offered four irregular fronts, of which the first, reckoning from the right of the town, extended from the Ebro to a convent of barefooted Carmelites, and was about three hundred yards wide. The second, twelve hundred yards in extent, reached from the Carmelites to a bridge over the Huerba. The third, likewise of twelve hundred yards, stretched from this bridge to an oil manufactory built beyond the walls. The fourth, being on an opening of four hundred yards, reached from the oil manufactory to the Ebro. [Sidenote: Rogniat’s Seige of Zaragoza. Cavalhero’s Siege of Zaragoza.] The first front, fortified by an ancient wall and flanked by the guns on the Carmelite, was strengthened by some new batteries and ramparts, and by the Castle of Aljaferia, commonly called the Castle of the Inquisition, which stood a little in advance. This was a fort of a square form having a bastion and tower at each corner, and a good stone ditch, and it was connected with the body of the place by certain walls loop-holed for musketry. The second front was defended by a double wall, the exterior one being of recent erection, faced with sun-dried bricks, and covered by a ditch with perpendicular sides fifteen feet deep and twenty feet asunder. The flanks of this front were derived from the convent of the Carmelites, from a large circular battery standing in the centre of the line, from a fortified convent of the Capuchins, called the Trinity, and from some earthen works protecting the head of the bridge over the Huerba.