Robert 'King' Carter was the wealthiest man in American prior to his death in 1732. He also freed his c132 slaves, and many of them seem to have drifted up into Frederick Co, VA to be the base of the large free-black population there. A researcher, Lorena Walsh from Colonial Williamsburg, has written a great book following them: From Calabar to Carter's Grove, and Col. Williamsburg is continuing the research(of course, now that Carter's Grove is up for sale I do not know what is happening). So Robert the younger followed his father's example.