6 April 20

On 5 April 1793, Congress approved William Thornton's architectural plan for the U. S. Capitol. "Construction of the Capitol began in 1793, with the initial cornerstone laid by President Washington on September 18, 1793, after holding a competition to determine the design of the building. The north wing was the first section completed, and the first session of Congress took place there on November 17, 1800." (From A Brief History of the U. S. Capitol Building.)