As Early advanced north and east toward Baltimore, Maryland, a Union force led by Maj. Gen. Lew Wallace met Early's forces and was defeated in the Battle of Monocacy on July 9, 1864. The cavalry brigade of the Second Corps, led by Brig. Gen. Bradley T. Johnson advanced further eastward into Maryland, led by cavalry forces under the command of Maj. Harry W. Gilmor. Upon reaching Westminster, Maryland, on July 10, Gilmor attacked Union cavalry forces, driving them out. Johnson's main cavalry force continued pressing Wallace's retreating Union troops, pursuing them into Cockeysville-Hunt Valley, Maryland, north of Baltimore, and then turned south destroying tracks and trestle bridges along the Northern Central Railway. Upon reaching Timonium, Maryland, Johnson divided the Second Corps cavalry brigade. He sent the commander of 2nd Maryland Cavalry, Maj. Gilmor, with a 135 detachment made up of both the 1st and 2nd Maryland Cavalry southeastward. The second part of Johnson's cavalry simultaneously turned south and headed toward the prison camp at Point Lookout, Maryland at the confluence of the Potomac River and the Chesapeake Bay.