On the night of the 23rd the French began their first parallel, on their right flank of the central hill, at a distance of 300 yards from the walls: the approaches to it needed no spadework, being completely screened by a ravine and a thick aloe hedge. The besieged shelled it on the succeeding day, but with small effect--only 3 workers were killed and 4 wounded. On the 24th a minor front of attack was developed on the left-hand hill, where a first parallel was thrown up about 250 yards from the walls. The gunboats on the southern shore fired on this work when it was discovered, but as it was invisible to them, and as they could only shoot at haphazard, by directions signalled from the town, they generally failed to hit the mark, and did little to prevent the progress of the digging. The besiegers only lost 4 killed and 25 wounded this day, and on the original point of attack were able to commence a second parallel, in which there was marked out the place for the battery which was destined to breach the town wall at the lowest point of its circuit, just south of the bed of the Retiro torrent. On the two following days the French continued to push forward with no great difficulty; they completed the second parallel on the centre hill, parts of which were only 180 yards from the town. On the left or eastern hill the trenches were continued down the inner slope, as far as the bottom of the ravine, so as almost to join those of the right attack. On the 26th a violent south-east gale began to blow, which compelled the British and Spanish gunboats to quit their station to the right of Tarifa, lest they should be driven ashore, and to run round to the west side of the island which gave them shelter from wind coming from such a quarter. The French works were, therefore, only molested for the future by the little 6-pounders on the north-east (or Corchuela) tower, and the heavy guns firing at a high trajectory from the island and the tower of Guzman. But the gale was accompanied by rain, and this, beginning with moderate showers on the 26th, developed into a steady downpour on the 27th and 28th, and commenced to make the spadework in the trenches more laborious, as the sappers were up to their ankles in mud, and the excavated earth did not bind easily into parapets owing to its semi-liquid condition. Nevertheless the plans of the engineers were carried out, and two batteries were finished and armed on the central hill, one lower down to batter the walls, the other higher up, to deal with the guns of the besieged and silence them if possible. The French lined all the advanced parallel with sharpshooters, who kept up a heavy fire on the ramparts, and would have made it difficult for the garrison to maintain a reply, if a large consignment of sandbags had not been received from Gibraltar, with which cover was contrived for the men on the curtain, and the artillery in the towers.