Controlling the river and railroad junction at Chattanooga was important to both North and South during the Civil War because it commanded important passes into Georgia and Alabama and could cut communications between the eastern and western parts of the state. Union forces advanced from Middle Tennessee in the summer of 1863, took control of Chattanooga, and marched into Georgia in September. After their defeat at the Battle of Chickamauga, about eight miles south of the Tennessee border, the Union army retreated to Chattanooga, where the Confederate army besieged it. Separate Federal attacks on November 24-25 drove Confederate forces from Lookout Mountain and Missionary Ridge and back into Georgia. In 1863-1864, Union soldiers built new fortifications along the region's rivers and rails, including Fort Hill overlooking the railroad in Cleveland, a temporary fort in a brick depot at Niota, and a temporary headquarters at Charleston on the Hiwassee River in an old post from the 1830s Trail of Tears.