SW 9 Intermediate Boundary Stone, also known as an Intermediate Stone of the District of Columbia, is a surveyors boundary marker stone, along what was once a boundary of Washington, DC, and now marks part of the boundary between City of Falls Church and Arlington County, Virginia (see: History of Washington, D.C.). It is within Arlington Countys Benjamin Banneker Park at the corner of North Van Buren Street and 18th Street North. It was named and was declared a National Historic Landmark in 1976 at the instigation of the Afro-American Bicentennial Corporation to honor Benjamin Banneker, who assisted in the land surveys that laid out Washingtons boundaries.   The stone was the first of the District of Columbia boundary markers to be listed on the National Register of Historic Places.
The boundary stone is a sandstone block about 1 foot (0.30 m) square in cross section, extending about 15 inches (38 cm) above ground and probably about 2 feet (0.61 m) below ground. The top is rounded and worn. Standardized inscriptions placed on each side of the stone are only partially visible, due in part to the stones sinking over time. 
The words Jurisdiction of the United States are inscribed on the northeast side, which faced the federal territory (once the District of Columbia; now Arlington County). The opposite side now facing the City of Falls Church contains the remnant of the word Virginia. Between those two sides, one side contains the year 1791, while the opposite side contains the remnant of an inscription recording the variation of the compass needle at the stones location (indicated as Var.). A brass marker was once mounted top of the stone, placed in early 1900s by the Daughters of the American Revolution; it has since been removed.
The stone is one of 40 boundary markers of the original District of Columbia. Benjamin Banneker (1731-1806) was an African American surveyor, mathematician and astronomer who assisted Andrew Ellicott during the first three months of