Matamoras, Mexico, April 26, 1846.

Sir: - It becomes my painful duty to inform you of the circumstances which led our being brought to this place as prisoners of war. Captain Thornton's command, consisting of fifty-two dragoons, left camp, as you know, at night on the 24th instant; it marched 15 miles and halted until daylight, when the march was again resumed. Captain Thornton's orders, as I understood them, were to ascertain if the enemy had crossed the river above our camp, and to reconnoitre his position and force. All his inquiries on the way tended to the conviction that the enemy had crossed in strength. About 23 miles from our camp our guide became so satisfied of this fact that he refused to go any further, and no entreaties on the part of Captain Thornton could shake his resolution. About three miles from this latter place we came to a large plantation bordering the river, and enclosed with a high chapparal fence, with some houses at its upper extremity. To these houses Captain Thornton endeavored, by entering the lower extremity, to approach; but failing to do so, he was compelled to pass round the fence, and entered the field by a pair of bars, the house being situated about 200 yards from the entrance. Into this plantation the whole command entered in single file, without any guard being placed in front, without any sentinel at the bars, or any other precaution being taken to prevent surprise. Captain Thornton was prepossessed with the idea that the Mexicans had not crossed; and if they had, that they would not fight. I had been placed in rear, and was therefore the last to enter. When I came up to the house I found the men scattered in every direction, hunting for some one with whom to communicate. At last an old man was found; and while Captain Thornton was talking with him, the cry of alarm was given, and the enemy were seen in numbers at the bars. Our gallant commander, immediately gave the command to charge, and himself led the advance; but it was too late; the enemy had secured the entrance, and it was impossible to force it. The officers and men did every thing that fearless intrepidity could accomplish; but the infantry had stationed themselves in the field on the right of the passage way, and the cavalry lined the exterior fence, and our retreat was hopelessly cut off. Seeing this, Captain Thornton turned to the right and skirted the interior of the fence, the command following him. During this time the enemy were shooting at us in every direction; and when the retreat commenced, our men were in a perfect state of disorder. I rode up to Captain Thornton and told him that our only hope of safety was in tearing down the fence: he gave the order, but could not stop his horse, nor would the men stop. It was useless, for by this time the enemy had gained our rear in great numbers. Foreseeing that the direction which Captain Thornton was pursuing would lead to the certain destruction of himself and men, without the possibility of resistance, I turned to the right and told the men to follow me. I made for the river, intending either to swim it or place myself in a position for defence. I found the bank too boggy to accomplish the former, and I therefore rallied the men, forming them in order of battle in the open field, and without the range of the infantry behind the fence. I counted twenty-five men and examined their arms, but almost every one had lost a sabre, a pistol, or carbine; nevertheless, the men were firm and disposed, if necessary, to fight to the last extremity. In five minutes from the time the first shot was fired, the field was surrounded by a numerous body of men. However, I determined to sell our lives as dearly as possible if I could not secure good treatment, and accordingly I went forward and arranged with an officer that I should deliver myself and men as prisoners of war, to be treated with all the consideration to which such unfortunates are entitled by the rules of civilized warfare. I was taken to General Torrejon, who by this time had his whole force collected in the field. I found that some prisoners had already been taken; which, together with those I had and those which were subsequently brought in, amounted to 45 men, exclusive of Lieutenant Kane and myself. Four were wounded. I know nothing certain of the fate of Captain Thornton and Lieutenant Mason: the latter I did not see after the fight commenced. I am convinced they both died bravely. The former I know was unhorsed, and killed, as I learn, in single combat, Romano Falcon. Lieutenant Mason's spurs were seen, after the fight, in possession of the enemy. The brave Sergeant Tredo fell in the first charge. Sergeant Smith was unhorsed and killed. The bodies of seven men were found, including, as I believe, the two officers above mentioned.

I was brought to Matamoras to-day about 4 o'clock, and I take pleasure in stating that since our surrender I and my brave companions in misfortune have been treated with uniform kindness and attention. It may soften the rigors of war for you to be informed fully of this fact. Lieutenant Kane and myself are living with General Ampudia: we lodge in his hotel, eat at his table, and his frank, agreeable manner and generous hospitality almost make us forget our captivity. General Arista received us in the most gracious manner; said that his nation had been regarded as barbarous, and that he wished to prove to us the contrary. Told Lieutenant Kane and myself that we should receive half pay, and our men should receive ample rations, and in lieu of it for to-day 25 cents a piece. On declining the boon on the part of Lieutenant Kane and myself, and a request that we might be permitted to send to camp for money, he said no; that he could not permit it; that he intended to supply all our wants himself. These promises have already been fulfilled in part.

I am, sir, very respectfully, your obedient servant,

W. J. HARDEE,
Captain 2d Dragoons.