Harry Gilmor's Confederate Cavalry, who were part of Jubal Early's invasion force.

Just before attacking Lew Wallace on the Monocacy River, Early sent most of his cavalry under Bradley Johnson to raid behind Union lines. Johnson split his force, with one group under Gilmor operating north of Baltimore, while Johnson attempted to get to Point Lookout to free the Confederate POWs.

Gilmor got up to about Harford County and Johnson got as far as Beltsville before Early called them back to cover his retreat after being stopped at the defenses of Washington.