Two pre-existing settlements were included in the territory, the port of
Georgetown, founded in 1751, and the
port city of
Alexandria, Virginia, founded in 1749. In 1791 and 1792, a team led by
Andrew Ellicott, including Ellicott's brothers
Joseph and
Benjamin and African American
astronomer Benjamin Banneker, whose parents had been enslaved, surveyed the borders of the federal district and placed
boundary stones at every mile point; many of these stones are still standing. Both Maryland and Virginia were
slave states, and
slavery existed in the District from its founding. The building of Washington likely relied in significant part on slave labor, and slave receipts have been found for the White House, Capitol Building, and establishment of
Georgetown University. The city became an important
slave market and a center of the nation's
internal slave trade.
