Fort Phantom Hill functioned briefly as a U.S. Army infantry post from 1851 to 1854, established on the Clear Fork of the Brazos to guard settlers and travelers along the Texas frontier defense line as part of a chain of forts stretching across the state. Conditions at the isolated post were harsh, with inadequate water, timber, and forage, and supply trains from Austin, roughly 250 miles away, were vulnerable to interception; disease further weakened the garrison. Most structures were simple jacal buildings, with only a handful of stone buildings such as the officers' quarters and commissary built more substantially. The Army abandoned the post in April 1854 as unsuitable for its purpose, and the buildings burned soon after, likely set by the departing troops. A few surviving stone structures found renewed use later in the decade when they were repaired and pressed into service as a stagecoach and relay station on the Butterfield Overland Mail route, which operated through the site from 1858 until the route was discontinued at the start of the Civil War in 1861. Today Fort Phantom Hill exists as a preserved ruins site rather than a functioning building complex, comprising three stone structures and roughly a dozen stone chimneys spread across a 38-acre tract. It was added to the National Register of Historic Places in 1972 and has been maintained since 1997 by the Fort Phantom Hill Foundation, which keeps the grounds open to the public as a free historic site and hosts periodic living-history events.