The design of this stamp publicized the international exposition which opened in San Antonio, TX, on April 6, 1968. The theme of the fair was "The Confluence of Civilizations in the Americas." This stamp also commemorated the 250th anniversary of the founding of San Antonio, which is a city and port of entry in south central Texas on the San Antonio River. It was founded as a Spanish presidio in 1718, and several missions, including the Alamo, were established nearby. The first civilian settlers came from the Canary Islands in 1731. The city played a prominent role in early Texas history. The Battle of the Alamo was fought there in 1836 during the Texas Revolution. Because of its location at the beginning of the Chisholm Trail, San Antonio was a major gathering point of cattle drives and it flourished during the late 19th century.