On what date was the cornerstone of the United States Capitol laid?

The cornerstone of the United States Capitol was laid on September 18, 1793.

President George Washington led the ceremony in the federal district, then commonly called Federal City. He was assisted by Joseph Clark, grand master of the Grand Lodge of Maryland, and participated in a Masonic ritual involving corn, wine, and oil. Washington struck the stone three times with a gavel.

Construction crews had begun excavating the Capitol’s foundations in July 1793. The cornerstone ceremony gave symbolic form to the government’s plan for a permanent national capital, even though the Capitol itself would take many years to complete.

The ceremony included Masonic visitors from Virginia, Maryland, Georgetown, and Federal City, along with the Alexandria Volunteer Artillery. A 15-gun salute represented the 15 states then in the Union. The original cornerstone materials and their precise later location became subjects of historical interest, while the Capitol continued to be expanded and rebuilt over the centuries.