A close reconnaissance at once convinced Lord Wellington that the defences had been amazingly improved--and, as time pressed, and the means of regular investment were but indifferent, he determined that the bastion of La Trinidad, from its unfinished counterguard,[6] should be battered. To effect this, the Picarina redoubt, forming nearly an angle with the bastion, and the lunette of San Rocque, must necessarily be carried. [6] _Counterguards_ are small ramparts, with parapets and ditches, erected in front of a bastion or ravelin, to secure the opposite flanks from being open to the covert-way. The night of the 16th March was bad enough to mask any daring essay, and rain, darkness, and storm favoured the bold attempt. Ground was accordingly broken, and though but one hundred and seventy yards from the covered way, the working parties were neither heard nor molested. The 17th and 18th were similarly employed, but under a heavy fire from the Picarina fort, and such of the guns upon the works as could be turned by the garrison on the approaches. The evening of the 18th, however, produced a very different scene, for the enemy became assailant, and a sortie was made with fifteen hundred men, accompanied by some forty cavalry. To the works, this sudden assault occasioned but little mischief. The gabions[7] were overturned, some intrenching tools captured, and great confusion caused among the working parties; but the French were speedily driven back, after causing much alarm, and a loss of one hundred and fifty in killed and wounded. Colonel Fletcher, the chief of the engineers, was unfortunately among the latter. [7] _Gabions_ are large circular baskets, filled with earth or sand, and used for forming parapets, covering working parties, &c., &c. The weather was in every way unfavourable for prosecuting the siege, and elemental influences seemed to have united with Philippon against the allied commander. The rain fell in torrents, the river rose far beyond its customary height, the pontoons swamped at their moorings, and all were swept away. From the violence of the current, the flying bridges worked but slowly, and serious apprehensions were entertained lest the communications should be interrupted with the other side, and, of necessity, that the siege must be raised. To forward the works required incredible fatigue; the ground was soaked with moisture, the trenches more than knee-deep with mud and rain, the revêtements[8] of the batteries crumbled away under any pressure, and it was almost impossible to lay platforms for the guns. Indeed, had the works been ready for their reception, the task of transporting heavy artillery across a surface, rendered a perfect swamp by the incessant torrents which had fallen for days without any intermission, would have been a most laborious duty. [8] _Revêtement_ of a battery is the exterior front, formed of masonry or fascines, which keeps the bank of the work from falling.