West Cornerstone of the Original District of Columbia

The boundary markers of the original District of Columbia are the 40 milestones that marked the four lines forming the boundaries between the states of Maryland and Virginia and the square of 100 square miles (259 km2) of federal territory that became the District of Columbia in 1801. Working under the supervision of three commissioners that President George Washington had appointed in 1790 in accordance with the federal Residence Act, a surveying team led by Major Andrew Ellicott placed these markers in 1791 and 1792. Among Ellicott's assistants were his brothers Joseph and Benjamin Ellicott, Isaac Roberdeau, George Fenwick, Isaac Briggs and an African American astronomer, Benjamin Banneker.