[3] In the spring of the year 1800, the capital of the United States was preparing to move from the well-established city of Philadelphia to a parcel of tidewater land along the Potomac River.

President John Adams issued an Executive Order on May 15 instructing the federal government to move to Washington and to be open for business by June 15, 1800.

The building was 147 feet (45 m) long and 57 feet (17 m) wide, flanking the south-east end of the President's House (later renamed the White House), one of four similar structures for the then four executive departments flanking the east (State and Treasury) and west sides (War and Navy) of the executive mansion facing Pennsylvania Avenue.

The fire-proof vault addition designed by Latrobe turned out to be a hearty structure – it was the only part of the building that survived the 1814 burning of Washington by British forces during the War of 1812.

Volunteers saved records that could be retrieved (mostly from the Latrobe vault extension which once again largely survived the fire) and the Treasury offices were relocated to a row of buildings on the south side of Pennsylvania Avenue, opposite the nearby Willard Hotel.

Walter's drawings for the first time showed a west wing of the Treasury building on the site of former greenhouses for the White House that would eventually create a closed rectangular shaped Classical Revival styled stone building with Mills's center wing bisecting the rectangle and creating two enclosed courtyards.

Key among his responsibilities was to merge the design approaches previously prepared for the addition of a south wing to the Treasury building extending over the site of the old State Department offices.

The inclusion of the later west wing in the design and planning created an opportunity for economies of scale by reducing costs for manpower and building materials.

Before the stoppage, the construction of the south wing had completed setting in place over 45 monolithic stone columns and pilasters, some weighing as much as 33 tons each.

[4]: 11 Sculptor James Earle Fraser created the statue of Alexander Hamilton, the first Secretary of the Treasury, which stands in front of the southern facade facing Alexander Hamilton Place and The Ellipse beyond, and the statue of Albert Gallatin, the fourth and longest serving Secretary, which stands before the northern entrance facing Pennsylvania Avenue, N.W.