The Alamo Mission in San Antonio attracts thousands of visitors each year. But many walk right over the literal line in the ground by the entrance without noticing it.

The origins of the metaphorical phrase “to draw a line in the sand” can be traced all the way back to antiquity, but in the United States, the idiom is usually associated with the siege of the Alamo, and the actual, fateful line that Colonel William Travis, commander of the Alamo defense forces, drew with his sword.

According to Texas legend, in the last days of the long battle for the Alamo, the mission was surrounded by the Mexican troops and defeat was certain. Travis had been told by the enemy commander to surrender or else his entire force would be killed. Knowing this, he gathered his men, took out his sword, and drew a line in the dirt. He asked his men to choose their fate: surrender and leave the Alamo, or cross the line and join him in defending the compound to the death, no turning back. According to the tale, all but one of the Texas Heroes joined Travis on the other side of the dirt line.

There is no proof that Travis actually made this gesture, or precisely where the line was drawn. But whether true or apocryphal, the dramatic story popularized the phrase, and through that, helps us remember the Alamo. To commemorate the event, a metal line and plaque were prominently placed on the ground in front of the doors to the Alamo. All of the defenders of the Alamo perished in the battle that ended on March 6, 1836.