After the disastrous losses at Chickamauga, the Union army retreated to Chattanooga. General Bragg arrived and occupied Lookout Mt., Missionary Ridge and Raccoon Mt., effectively surrounding General Rosencrans and the city. He cut off the main supply routes and laid siege when Rosencrans did not evacuate. Bragg's cavalry units attacked the only supply route left to the Union- the tortuous route through the Sequatchie Valley. Bragg fails to capitalize on his advantages and, when Washington relieves Rosencrans of command, Ulysses S. Grant would break the siege by sweeping the Confederate forces from Lookout Mountain and Missionary Ridge.