The "Texian" forces who had re-fortified the Alamo were volunteer (war duration or two years) soldiers and regulars (two year service) of the Provisional Government, lead by Henry Smith. Sam Houston was to be the major general and commander-in-chief under the authority of the governor. The Provisional Government was often at odds with Governor Smith. The two sides clashed over politics and decision. The Matamoros Expidition led to Smith being voted out of office and replaced with Lieutenant-Governor James Robinson. This squabble was a total embarassment to the Texas government while the rebellion needed them the most. The Texan Army never was larger than 2,000 men at the time of the Alamo siege. With the successive losses at Goliad, Refugio, Matamoros and San Antonio, the army was reduced to about 1,000 men.
The Alamo protected the road farther northeast into Texas. Although the Alamo was not designed for military purposes, the Texian militia and regulars under Green B. Jameson, fortified the post and mounted 18 cannon , including an 18 pounder (8 kg). This was the greatest concentration of cannons west of the Mississippi River at one place. The Mexican forces would not be able to bypass the post and use the road without investing and taking the Alamo.
The defenders of the Alamo came from many places besides Texas. The youngest, Galba Fuqua, was 16, and one of the oldest, Gordon C. Jennings, was 57. They came from twenty-eight different countries and states. One group, the New Orleans Greys , came from the city of that name to fight as infantry in the revolution. The two companies comprising The Greys participated in the Siege of Bexar(Dec.1835). Most Greys then left San Antonio for an expedition to Matamoros with the promise of taking the war to Mexico and plundering the city, but about two dozen remained at the Alamo. After the battle of the Alamo, the company flag was captured and sent to Mexico City as proof of U. S. involvement. It is now the property of the National Historical Museum in Mexico City .No one knows which flag flew over the Alamo during the battle. One flag of note was the Mexican tri-color flag with the numbers "1824" set in the middle denoting the Constitution of 1824. Another flag might have been the Mexican tri-color with two stars in the middle denoting Coahuila y Texas. The flag issue thus remains unsolved.
From Tennessee , came another small group of volunteers led by former Tennessee Congressman David Crockett . The Tennessee Mounted Volunteers as they were called arrived at the Alamo on February 8 , 1836 .
The Mexican Army arrived on February 23 , 1836 and was a mixed force of regular infantry and cavalry units as well as activo reserve infantry battalions . They were equipped with the British Baker and the out dated, short range but effective and deadly British "Tower Musket, Mark III or Brown Bess musket and were well-drilled, though the Mexican army discouraged individual marksmanship. The initial forces were equipped with four of seven inch (178 mm) howitzers, seven of four pounders (1.8 kg), four of six pounders (2.7 kg), four of eight pounders (3.6 kg) and two of twelve pounders (5 kg) cannon: Several of the Mexican officers were European mercenary veterans , (Filisola-Italy), (Antonio Gaona-Cuba) and General Santa Anna was a veteran of the Mexican War of Independence . The Mexican siege was scientific and professionally conducted in the Napoleonic-style. The Mexican army was about four times larger than the U.S. Army. The average Mexican soldier stood 5'1".