Factual error: Approximately 2 hours and 10 minutes into the "restored" full-length video version, there's a birthday party for little Lisa Dickinson, and the Alamo defenders sing "Happy Birthday" to her. The Alamo battle happened in 1836. According to David Ewen's "All the Years of American Popular Music," the song "Happy Birthday to You" was composed and copyrighted by sisters Patty and Mildred J. Hill, first as "Good Morning to All," in 1893.
Factual error: The movie's opening scene manages to get wrong almost every historical detail except the names. Sam Houston was never in San Antonio with Colonels Neill, Travis, and Bowie. Then-governor Henry Smith - not General Houston - made Travis a colonel (in December). Bowie did a lot of drinking and carousing, but that never caused him to be demoted or to lose a command. Bowie did marry into the Mexican aristocracy, and he acquired a lot of land, but it would have been ridiculous for Travis to therefore doubt his loyalty to the rebellion. Bowie was one of the rebellion's best-known firebrands and had just taken San Antonio from the Mexicans.
Revealing mistake: When Crockett, Bowie and their men are about to destroy the giant cannon, several of the men are standing right next to it at the moment one of them tosses the torch on the touch hole. Then, there's a big flash at the touchhole. In the very next shot, right before the cannon explodes, we see the cannon, but everyone has disappeared. There was no time for them to flee completely out of sight.
Plot hole: The morning of the final battle, the sun rises behind the mission, silhouetting a sentry. When the ending credits roll, the sun sets behind the mission.
Factual error: When Bowie first walks into the chapel, you can see all the way back to the eastern wall. By this time, there would have been a dirt ramp leading up to two 12-pound cannon that overlooked the wall. In the same scene, the doorway to Bowie's left is where the powder magazine would have been, and to the right is where the women and children were. In the movie, these uses for the rooms are reversed.
Plot hole: At the start of the final battle, the Mexican artillery is lined up wheel to wheel, and fires the opening salvo. Apparently Newton's third law doesn't apply in Texas, because none of the cannon recoil after firing.
Factual error: When the scout comes in and describes a huge cannon the Mexicans have, there are actually two mistakes, one of continuity and one historical. The continuity mistake involves the powder horn the scout is wearing. When you first see him it is facing with the tip one direction. The scene then cuts to Bowie. When it cuts back to the scout again the powder horn is turned the opposite direction. The historical mistake involves the cannon itself. The largest cannon used in the battle was in possession of the Alamo defenders. Santa Anna brought only small field pieces on the winter march from Mexico. (00:30:00)
Continuity mistake: In the scene on the last assault on the Alamo, Mexican cavalry (in red coats) jump the palisade next to the chapel and are killed by a volley of musketry and their bodies are littered everywhere. Next time you see the area, however, the bodies have disappeared.
Other mistake: During the final assault, a man falls mortally wounded on a cannon wheel and shouts for Crockett to come over. Crockett is standing doing nothing with Beekeeper, in an action in where the defenders are largely out numbered. Shouldn't every man be fighting not standing around watching?
Factual error: Bowie's wife had died in 1833, and from cholera, not plague. Her two sisters actually joined Bowie in the Alamo.