This fort was a Civil War earthwork fortification on the east shore of Matagorda Island constructed to guard Cavallo Pass, the entry to Matagorda Bay. It was built in 1861 when it was determined that Fort Washington, a small fort near the lighthouse on Matagorda Island was too exposed. On November 29th, 1863, the Confederates, outnumbered and outflanked, evacuated the fort and it was occupied and repaired by Union forces and they used it as a base of operations for other campaigns in the area. In the spring of 1864, Union troops withdrew from Matagorda Bay and the fort was then reoccupied by the Confederates and held until the end of the war. Eastern walls of the fort were destroyed as the shoreline was eroded by a storm in 1868. By 1878, the rest of the 9-foot-high, 20-foot-thick, turf-covered walls had eroded away. Outlying emplacements and rifle pits can still be traced in some areas. Nothing else remains.
"Texas became increasingly important toward the end of the war because it was one of the last holdouts and one of the last conduits of cotton - much of it moving through Mexico," says Texas historian Doty Freeman Smith. "The Federals' interest in cutting off that trade remained high throughout the war. That's why we had blockades of the Texas coast until early 1865."