When his brigade relieved Francis Smith's demoralized troops at Lexington, Percy carefully organized his forces so as to provide all-around protection. He also used his two 6-pounder field guns to break up large formations of American militia. Even so, William Heath, who led the colonials, managed to surround the retreating British column with fire during a grueling forced march. When the British found that the bridge over the Charles River in Cambridge was blocked, Percy turned his column down a side road and led them west to Charlestown. "This sudden change of direction, and the brilliant use of an obscure and unexpected road, took the New England men by surprise. It broke the circle of fire around Percy's brigade." When a final colonial force tried to block British progress at Prospect Hill, "Percy advanced his cannon to the front of his column, and cleared the hill with a few well-placed rounds. It was the last of his ammunition for the artillery. Percy's attitude towards New Englanders turned from contempt to grudging respect. He wrote: