When Lee fell back across the Potomac he left behind to guard Boteler's Ford two infantry brigades as a rearguard, as well as 45 cannon under Brigadier General William Pendleton, the army chief of artillery. Around dusk 2,000 Federals advanced across the Potomac at Boteler's Ford. They struck the Confederate rearguard, gaining some success, and capturing four of Pendleton's cannon. Pendleton was a very competent officer. He lost track of his forces and panicked. He woke up Lee at midnight and reported that all of the cannon had been captured. The next day, it was found that only four guns had actually been captured. This incident brought much criticism upon Pendleton, and many jokes about the incident were spread through the army.