In September 1863, Union Gen. Ambrose E. Burnside led his army toward Knoxville along the East Tennessee & Georgia Railroad to take control of the strategically vital city. At Niota, his men converted the brick depot, the state's oldest, constructed in 1854, into a temporary fort by removing bricks at shoulder height to make gun ports, and they scribbled their names, still visible, on the walls in the baggage area. They also guarded Sweetwater. The nearby Great Craighead Cave, now called Lost Sea Cave, served as a saltpeter mine for the Confederate gunpowder industry from 1861 until the Federals arrived in 1863. Charles W. Hicks later wrote that he and others "camped there and worked faithfully two years and a half until the Federal soldier came to Sweetwater ... when we tore down our works and scattered to our homes." Union Col. Frank L. Wolford commanded a garrison at Philadelphia to protect the tracks there. On October 20, 1863, Confederate forces under Gen. George G. Dibrell and Col. J. J. Morrison overran the position, captured six mountain howitzers, and achieved the first Confederate victory of the Knoxville Campaign.