Two pre-existing settlements were included in the territory: the port of Georgetown, Maryland, founded in 1751, and the port city of Alexandria, Virginia, founded in 1749. During 1791–92, a team under Andrew Ellicott, including Ellicott's brothers Joseph and Benjamin and African-American astronomer Benjamin Banneker, surveyed the borders of the federal district and placed boundary stones at every mile point. Many of the stones are still standing.