After the Battle of Chickamauga in September 1863, Union Gen. William S. Rosecrans retreated to Federal-occupied Chattanooga, a strategically vital rail center, where Confederate Gen. Braxton Bragg laid siege from Lookout Mountain and Missionary Ridge. Union Gen. Ulysses S. Grant took command in October and began efforts to break the siege. By the end of October, the Federals had opened the "cracker" or supply line at various points on the Tennessee River, and food, supplies, and reinforcements began to arrive in the beleaguered city. Bragg detached forces under Gen. James Longstreet to attack Knoxville as a diversion. Late in November, Union Gen. William T. Sherman led veterans from the Vicksburg campaign toward Chattanooga, marched past the city, crossed a pontoon bridge over the Tennessee River, and disappeared into the hills of Stringer's Ridge north of the city so Confederates would believe he had continued to Knoxville. The ruse worked, and Sherman's advance units arrived near here on November 21, with the rest of the command in camp by November 23, unobserved by Confederate forces. Early the next morning, Sherman marched his men 2 miles east to the Tennessee River, crossed over a pontoon bridge, and assaulted the northern end of Missionary Ridge later that day. By evening, his force occupied vital ground on the ridge, contributing to the Union victory the next day, after which Bragg retreated and the Union army held Chattanooga for the rest of the war.