Glad you asked, Paul! To find the answer, we put our Googling skills to the test.
Turns out, the pillar is actually a gatepost dating back to 1814. It’s one of four identical structures and a gatehouse at 15th and 17th streets farther west on Constitution Avenue. According to the District of Columbia Inventory of Historic Sites, a list of the city’s historic landmarks published by the DC Department of Consumer and Regulatory Affairs, the sandstone pillars and gatehouse originally composed a gate on the west side of the Capitol grounds. They were installed as part of the reconstruction effort following the War of 1812, in which the British burned the Capitol building.
The gate was designed by Charles Bulfinch, a Harvard graduate and self-trained architect who split his career between projects in Boston and Washington. In addition to the gate, Bulfinch planned the Capitol grounds and the original west terraces, and he designed and constructed the dome and original rotunda of the US Capitol. In 1818, he was appointed Commissioner of Public Buildings by President James Monroe.
The Bulfinch Gateposts, as the pillars are known today in history books, were removed from the Capitol grounds in 1874 and deposited at their current locations in 1880. After weathering several floods and deterioration from acid rain, the gateposts were restored in 1940. In 1973, they were added to the National Register of Historic Places.
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