The Old San Antonio Road, popularly known as El Camino Real, was one of Texas’s oldest and most significant trans-Texas routes, but rather than a single fixed road it was a changing network of Indian trails, natural stream crossings, and exploration routes that served commerce, migration, and communication during the Spanish colonial period. Its various segments shifted over time in response to weather, Indian relations, terrain, transportation, settlement, and military needs. The first known trans-Texas journey along this network was recorded in 1691, when the Teran-Mazanet expedition crossed the Rio Grande and followed the Camino de los Tejas into far East Texas, while other segments, including the portions connecting Bastrop and Crockett after 1790 and Nacogdoches and Alto about 1830, appeared later. Earlier Spanish entradas used the more westerly upper route, and the gradual southeastward shift of the Presidio del Rio Grande Road through the 18th and 19th centuries may have reflected the Apache and Comanche threat to Spanish travelers. These caminos reales were major factors in the conquest and colonization of pre-Republic Texas, especially after French efforts such as La Salle’s 1685 colonizing attempt alarmed Spanish authorities and led to military expeditions northward across the Rio Grande. Communities were founded as way stations between these outposts and Presidio del Rio Grande, with San Antonio de Bexar becoming the first and the regional hub. Until Mexico gained independence in 1821, Spanish officials tried to strengthen Texas by encouraging civilian settlement between Bexar and Nacogdoches, and frontier routes shifted to serve those settlements. What had been intended as a defensive artery also became a conduit for resistance to Spanish rule, and the evolving road network influenced the strategy of the Texas Revolution. After the Republic of Texas was established, immigrants from the U.S. entered along many routes, including this one. Following the Mexican-American War, the Camino de Arriba, now called the Old San Antonio Road, regained prominence by guiding travelers from East Texas to San Antonio during the Gold Rush, and during the War Between the States it again became important for transporting cotton and for moving troops and supplies between East Texas, San Antonio, Laredo, and Louisiana. After the Civil War and the resulting economic decline, large sections of the old Spanish roads were abandoned for shorter routes to new markets, and the remaining segments served chiefly local purposes. Its lasting importance lies in its role within the oldest transportation, communication, and military network in Texas, linking the Spanish colony, the republic, and later the state, serving as a post road long before the Republic of Texas developed post roads, as a cattle trail long before the Chisholm Trail, as a military road connecting forts on New Spain’s northern frontier, and ultimately as a principal avenue of immigration for Anglo-Americans who helped forge a new Texas.