The Battle of Allegheny Mountain took place on December 13, 1861, in Pocahontas County and was one of the bloodiest battles of the Civil War's first year. Union Gen. Robert Milroy led 1,900 men in an attack on about 1,200 Confederate soldiers camped on Allegheny Mountain.

Milroy split his force into two groups to attack both sides of the Confederate camp. The first group attacked at daybreak but was pushed back after hours of fighting. The second group also failed to break through. Union forces suffered 140 casualties; the Confederates had about 128 casualties and 34 captured or missing.

Although the Confederates had planned to leave the mountain, the failed Union attack convinced them to stay through the winter.