As Mexican Hippie points out, it's also Aggie Muster, which is a very emotional day for Aggies. It's part of the Aggie tradition to remember those who have passed on to the next life during the past year. Started, I believe, on Corrigidor by the American troops holding out against the Japanese in WWII.
April 21, 1836 On this day in 1836, Texas forces won the battle of San Jacinto, the concluding military event of the Texas Revolution. Facing General Santa Anna's Mexican army of some 1,200 men encamped in what is now southeastern Harris County, General Sam Houston disposed his forces in battle order about 3:30 p.m., during siesta time. The Texans' movements were screened by trees and the rising ground, and evidently Santa Anna had no lookouts posted. The Texan line sprang forward on the run with the cries "Remember the Alamo!" and "Remember Goliad!" The battle lasted but eighteen minutes. According to Houston's official report, the casualties were 630 Mexicans killed and 730 taken prisoner. Against this, only nine of the 910 Texans were killed or mortally wounded and thirty were wounded less seriously.
"Measured by its results, San Jacinto was one of the decisive battles of the world. The freedom of Texas from Mexico won here led to annexation and to the Mexican-American War, resulting in the acquisition by the United States of the states of Texas, New Mexico, Arizona, Nevada, California, Utah and parts of Colorado, Wyoming, Kansas and Oklahoma. Almost one-third of the present area of the American Nation, nearly a million square miles of territory, changed sovereignty."