By this time the works opposite Matamoros were well advanced, yet, owing to the peculiar nature of the country and our deficiency in the proper description of light troops, we were kept in ignorance of the enemy's movements on the left bank. It was ascertained, however, with sufficient certainty, that they were continuing to throw considerable forces on the eastern shore, with the design of attacking our command; and General Taylor received information, upon which he could rely, that Arista had prepared to pass the Rio Grande, below Matamoros, in order to effect a junction with his forces from above. It was not believed, however, that he would assault the position opposite that city even with four thousand men, and hence our commander-in-chief supposed that the depot at Isabel was the object of his movement. This impression was strengthened by the fact that since a rigid blockade of the river was maintained, provisions had become exceedingly scarce at Matamoros; and, therefore, hastening the completion of the field work, he was able by great exertions on the part of our troops, to bring it to a good state of defence by the first of May. The seventh infantry under Major Brown, Captain Lowd's and Lieutenant Bragg's companies of artillery, together with the sick of the army, were left in the work; and, on the afternoon of that day, General Taylor moved with the main force under his immediate command in the direction of Point Isabel. At eleven o'clock, the army, by a rapid march, was enabled to bivouac on the prairie at a distance of ten miles from the depot, and on the next day, it reached its destination without encountering the enemy, though the scouts surprised and shot several men belonging to the Mexican pickets. On the morning and during the day of the 3d of May, a heavy cannonade in the direction of Matamoros announced to General Taylor that an attack had probably been commenced on the American fort. This was a different result from his anticipations, and made him extremely anxious for the fate of the small but brave command that had been left, with slender supplies of rations and ammunition, in the incomplete field work. Accordingly, on the evening of that day, a squadron of one hundred dragoons under Captain May, accompanied by Walker and ten of his daring rangers, was despatched to pass, if possible, through the hordes of Mexican guerillas that lined the road. They were ordered to proceed within a few miles of Fort Brown and reconnoitre the country on the left towards the river; next to take a position on the edge of the chapparal, and, if the commander heard no firing from our fort, he was then to despatch a small command under Walker to communicate with Major Brown. After this he was to await the return of the gallant rangers, and repair to Point Isabel.