On September 9, part of the Army of Northern Virginia's artillery under Colonel R. L. Walker escorted by Col. Elijah V. White's Battalion entered Loudoun county at Point of Rocks after unsuccessfully trying to destroy the C&O Canal aqueduct over the Monocacy River.

At about the time the Battle of Antietam was occurring, Lt. Col. Hugh Judson Kilpatrick, commanding ten companies of cavalry, left Washington to reoccupy Leesburg and clear the area of any remaining Confederates.

Upon arriving in Leesburg, Kilpatrick found the town held by Company A of the 6th Virginia Cavalry, forty or so infantrymen under the command Captain Gibson, and Colonel White and thirty of his troopers.

Thinking the area was clear of Federals and safe to raid, Captain Treyhorn, a new addition to the company, led a scouting party towards Berlin, Maryland (present day Brunswick), stopping in Lovettesville for the night on the 19th.

The Federals, however, took notice of the Confederates, and General John Geary was dispatched from Harpers Ferry with two infantry brigades and 300 men from the Col Thomas Devin's 6th New York Cavalry Regiment to engage the scouting party.

As Devin mounted a charge and Geary hit the flank of the 35th, Treyhorn deployed sharpshooters on top of nearby haystacks, who momentarily kept the infantry at bay, but before long the 35th was forced into a full retreat that quickly devolved into a rout that was only ended when the horsed of the 6th New York became too fatigued to continue the chase.