Saint Patrick's Battalion Remembrance Day is observed in Mexico every September 12. This day honors the immigrants and expatriates of European descent, primarily Irish, who fought alongside Mexico during the Mexican-American War and were executed by American soldiers. The battalion, known as the San Patricios, was formed by John Riley and Patrick Dalton, consisting mainly of Catholic Irish and German immigrants who had deserted the U.S. Army, along with other immigrants and escaped slaves. They participated in significant battles, including the Battle of Churubusco, where many were captured and subsequently tried for desertion, leading to the hanging of fifty battalion members between September 10 and 13, 1847. While September 12 is not an official memorial day, it is commemorated in various cities and towns across Mexico, alongside March 17, which is celebrated as Saint Patrick's Day.