Who helped design the city of Washington DC?

Answer 1

Benjamin Banneker.

While Andrew Ellicott and his team were conducting the federal district boundary survey, Pierre (Peter) Charles L'Enfant was preparing a plan for the federal capital city (the City of Washington), which would be located in a relatively small area bounded by the Potomac River, the Anacostia River (known at the time as the "Eastern Branch"), the base of the fall line and Rock Creek at the center of the much larger 100-square-mile (260 km2) federal district. In late February 1792, President George Washington dismissed L'Enfant, who had failed to have his plan published and who was experiencing frequent conflicts with the three Commissioners that Washington had appointed to supervise the planning and survey of the federal district and city.

According to a Banneker legend, L'Enfant took his plans with him after his dismissal, leaving no copies behind. As the story is told, Banneker spent two days reconstructing the bulk of the city's plan from his presumably photographic memory. According to the story, the plans that Banneker purportedly drew from memory provided the basis for the later construction of the federal capital city. Titles of works relating this fable have touted Banneker as "The Man Who Saved Washington" and "An Early American Hero".

Answer 2

It was Pierre Charles L'Enfant, an architect, who designed how the streets would be laid out. Washington, D.C. became America's capital in 1790.