General Albert Sidney Johnston, having arrived in Houston from a visit to his home, children, and relatives in Louisville, Kentucky, only a few hours before news of the Mexican seizure of San Antonio had come in,[17]  was ordered by the new Secretary of War, Barnard E. Bee, to take charge of the military operations on the western frontier. He was to proceed to the frontier with troops under the expectation that Congress at its next session would meet the necessary expenses incurred in "humbling an arrogant, a cowardly and contemptible foe." "We have long been contented," declared the editor of the Telegraph, "with merely defying the power of Mexico; we should now teach her, that she can no longer even threaten with impunity."[18] 

Johnston called out a portion of the militia and ordered it and the volunteer companies being formed in various parts of the Republic to march to the relief of Béxar. The militia and volunteers from Harris County and the east were to rendezvous at Mercer's Crossing on the Colorado.[19]  By the 30th, organization of the militia was proceeding rapidly in Harris County, and sixty mounted volunteers were on the eve of making their departure for the west.[20] 

On the 30th news reached Houston from New Orleans that the captain of the United States sloop-of-war Natchez had just returned from Matamoros with important information concerning the Mexican invasion plans. He reported the arrival at Matamoros of 600 soldiers from the interior of Mexico on November 22, and stated that a battalion of infantry consisting of some 200 men had crossed the Río Grande that day and had taken up their line of march for Texas with two pieces of artillery; and that on the following day a battalion of 350 cavalrymen had crossed the river and joined the infantrymen preparing to advance upon Texas. Four days later (November 27), a battalion of sappers crossed the Río Grande with the intention of joining the others, then advancing toward the Arroyo Colorado, where some 1,200 men were stationed.[21]