From 1791 to 1792, at the request of Secretary of State Thomas Jefferson, Ellicott worked under the direction of the three commissioners that President George Washington had appointed, surveying the boundaries of the federal Territory of Columbia, which would become the District of Columbia in 1801, containing the Federal City also then becoming known as "Washington City". He was assisted in this survey first by the free African-American astronomer Benjamin Banneker and then by Ellicott's brothers, Joseph Ellicott and Benjamin Ellicott. Ellicott's team put into place forty boundary stones approximately 1 mile (2 km) apart from each other that marked the borders of the Territory of Columbia of (see: Boundary Markers of the Original District of Columbia). Most of these stones remain in their original positions. As engravings on many of the stones still show, Ellicott's team placed those that marked the southwestern /southeastern border with Virginia in 1791, and those that marked the northwestern / northeastern border with Maryland in 1792.