At the Prospect Hall mansion off Jefferson Street to Buckeystown Pike near what is now Butterfly Lane, in the early morning hours of June 28, 1863, a messenger arrived from President Abraham Lincoln and General-in-Chief Henry Halleck, informing General George Meade that he would be replacing General Joseph Hooker after the latter's disastrous performance at Chancellorsville in May. The Army of the Potomac camped around the Prospect Hall property for the several days as skirmishers pursued Lee's Confederate Army of Northern Virginia prior to Gettysburg. A large granite rectangular monument made from one of the boulders at the "Devil's Den" in Gettysburg to the east along the driveway commemorates the midnight change-of-command.