Fort Lancaster functioned as a U.S. Army infantry post established in 1855 to guard the San Antonio-El Paso road and the nearby Pecos River crossing, protecting mail carriers, wagon trains, and settlers traveling through the rugged terrain of what is now West Texas. The garrison built and maintained more than thirty structures, including a blacksmith shop, hospital, sutler's store, and bakery, supporting the routine logistics and daily life of frontier soldiering in an isolated, arid environment. Federal troops abandoned the post at the outset of the Civil War, and Confederate forces briefly occupied and used it before it was left vacant again; the U.S. Army did not permanently reoccupy it afterward. In December 1867, Buffalo Soldiers of the 9th Cavalry's Company K, stationed there after the war, repelled a large attack by several hundred Native American warriors and associated raiders, an engagement notable as one of the few direct assaults on a Texas Army post. The fort was abandoned for good shortly thereafter as the military frontier shifted. Today the roughly 82-acre site is preserved by the Texas Historical Commission as a state historic site, with stabilized stone ruins of the fort's buildings left largely as found, walking trails through the grounds, and a visitor center and museum that interpret the post's role in guarding the frontier road and river crossing.