The original building was completed in 1800 and was subsequently expanded, particularly with the addition of the massive dome, and expanded chambers for the bicameral legislature, the House of Representatives in the south wing and the Senate in the north wing. Like the principal buildings of the executive and judicial branches, the Capitol is built in a distinctive neoclassical style and has a white exterior. Both its east and west elevations are formally referred to as fronts, though only the east front was intended for the reception of visitors and dignitaries.

Answer this question: when was the united states capitol building built? Let's give stream of consciousness first:
To answer the above question, the relevant sentence is: The original building was completed in 1800 and was subsequently expanded, particularly with the addition of the massive dome, and expanded chambers for the bicameral legislature, the House of Representatives in the south wing and the Senate in the north wing.
So, the final answer is 1800.