The soldiers sing "Happy Birthday to You" to a little girl, 57 years before it was written. (This song is only heard in the longer "Director's Cut" version of the film on VHS or LaserDisc, not the generally available 160 minute DVD version.)
The movie makes an attempt to recreate the iconic bell-shaped facade of the church, but in fact, that was not added until 1850 by the U.S. Army. At the time of the battle, the roof of the church was flat all the way around the entire structure.
When a soldier is riding his horse, we can hear the horses hoofs clopping on the ground. When the horse jumps into the air to jump over a fallen log, we can still hear the clopping noise even when the horse is in mid-air.
The character played by Linda Cristal is called 'Flaca' several times, 'Graciela' by Emil and 'Maria de Lopez y Bejar' by Crockett. While 'Flaca' is obviously a nickname (it means "thin one" in Spanish), the first name inconsistency is never explained.
When Capt. Dickinson announces to Col. Travis that Bowie is approaching, there is a soldier on the Travis' right-hand side pulling up a cannon by a rope. It cuts to the next shot and the same soldier appears only gesticulating to orient whom actually is pulling the rope. Then, from one shot to another, the cannon appears on the wall.
When the Mexicans begin the siege of Alamo, Col. Travis uses a lunette to watch them, while Capt. Dickinson takes notes on his left-hand side. Between shots, seen from behind, Dickinson is on the Travis' right hand side.
At the end of the film, when Lisa Dickinson is being led away from the Alamo on a mule, a large smudge appears on her left cheek when she is being led past Santa Anna that was not present when she was placed on the mule.
At the beginning of the movie after the meeting at the Alamo Sam Houston is riding away. Behind him is the character Jocko riding a mule. Later, Jocko is one of the defenders saying a final goodbye to his family.
Talking to Crockett, Flaca grabs the window wide open grates with her both hands. In the following shot, shown from inside, she is leaning the right part of her body on the window and maintaining only the left hand on the grate.
When Crockett and his men arrive at the Alamo, and he is standing in front of his men, Beekeeper is several feet back dismounting his horse. When the camera angle changes, he is standing right behind Crockett.
When Beekeeper takes the guitar from the Mexican in the cantina, the musician is clearly holding it left-handed, yet Beekeeper takes it right-handed and proceeds to apparently play and sing: not impossible but highly unlikely.
While planning the Alamo's defense with Crockett and Bowie, Travis says Fannin is coming to their aid from Goliad and "will move south by the first of the week." Goliad is south of San Antonio. To help the Alamo, Fannin would need to move north.
Jim Bowie is shown in bed suffering from injuries received in an explosion during the siege. In reality, throughout the siege he was bedridden because of an illness believed to be pneumonia, typhoid or tuberculosis.
The opening scene of the movie shows Sam Houston giving orders to William Barrett Travis to hold off the Mexican army until he could build an army. In reality he sent Travis to the Alamo to help Jim Bowie burn it down and retreat to Gonzales, Texas. Bowie and Travis ignored the order.
Col. Travis' last speech in the plaza asking for those who would to stay to the end did not show him draw a line in the sand with his sword. In reality two survivors, Moses Rose and Susannah Dickenson both reported he did.
After the first major skirmish, a rider arrives and notifies Travis and the others that Colonel Fannin would not be coming with reinforcements as he and his men had been ambushed and murdered. In fact, Fannin and his men were captured and murdered in the town of Goliad, TX three weeks after the Alamo had fallen.
When Travis is killed he falls to the ground face down. As the Mexican soldiers overrun that position, one of them kicks Travis's hand. Some people think incorrectly that this is actor Harvey deliberately moving his hand to avoid being stepped on.
Just prior to an explosion on the wall during the first battle, several Texans are seen from behind watching the Mexican attack. One of the "Texans" is an obvious wooden dummy, costumed and placed to absorb the greatest impact of the explosion.
During the first attack by the Mexicans, you can see the Alamo's right side window (by the fence) is black after being burned from the huge explosion at the end of the film. This is clearly seen when they show a close up of Crockett at the fence area.