As soon as Ampudia assumed the command he ordered all Americans to leave Matamoros within twenty-four hours for Victoria, a town in the interior of Tamaulipas; and on the twelfth of April he addressed a note to General Taylor requiring him, within the same peremptory period of time to break up his camp, and retire to the other bank of the Nueces, whilst their respective governments were deciding their quarrel by negotiation. He informed our commander that if he persisted in remaining on the alleged soil of Tamaulipas, arms, alone, could decide the dispute, but that the war, which would necessarily ensue, should be conducted, upon the part of Mexico, conformably to the principles and rights established by the civilized world. General Taylor did not delay his reply. On the same day he answered the Mexican chief, that inasmuch as he was charged with the military and not the diplomatic duties of the controversy, he could not discuss the international question involved in the advance of the American army, but that he would unhesitatingly continue to occupy the positions he held at Isabel and opposite Matamoros in spite of all menaces. The hostile declarations and alternative presented by Ampudia induced Taylor to order the stringent blockade of the Rio Grande, so as to stop all supplies for the city, and the naval commander at the Brazos de Santiago was directed to dispose his forces accordingly. A body of Texan rangers, under the command of Captain Walker, a tried and daring soldier of the frontier, was stationed on the road to Point Isabel. During the night of the 27th and 28th of April, the troops, at the latter place, consisting chiefly of two companies of artillery, under the command of Major Monroe, were in momentary expectation of attack in consequence of rumors from the enemy, for it was known that large bodies of Mexicans had crossed the river and were striving to interpose themselves between Isabel and the fort opposite Matamoros in order to cut off supplies for the garrison. Several teams that departed from the depot for the fort were forced to return, and, on the morning of the 28th the camp of Walker was surprised on the prairie by a party of bold rancheros who killed five of our rangers and dispersed the rest, while the officer of the company and half of his command were absent on detached service.