Description:
According to the CWSAC summary:
During the night of July 4-5, Lee’s battered army began its retreat from Gettysburg, moving southwest on the Fairfield Road toward Hagerstown and Williamsport, screened by Stuart’s cavalry. The Union infantry followed cautiously the next day, converging on Middletown, Maryland. On July 7, Imboden (CS) stopped Buford’s Union cavalry from occupying Williamsport and destroying Confederate trains. Kilpatrick’s cavalry division drove two Confederate cavalry brigades through Hagerstown before being forced to retire by the arrival of the rest of Stuart’s command. Lee’s infantry reached the rain-swollen Potomac River but could not cross, the pontoon bridge having been destroyed by a cavalry raid.
Wikipedia -
http://en.wikipedia.org/wiki/John_D._Imboden