The Brushy Mountain Line or Lost Mountain Line was a military fortification line protecting Atlanta during the American Civil War.

It was built around June 1864, by the Confederate army in Cobb County early in the Atlanta Campaign to defend the city from an invasion by Union troops. Its eastern end was at Brushy Mountain north of Marietta and southeast of Big Shanty. The west-southwest end was first at Lost Mountain, then was moved east along Mud Creek.

A Georgia state historical marker is located on the road shoulder of U.S. 41 northbound, just south of Greer's Chapel and Barrett Parkway.

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