Construction of the U. S. Treasury Building ca. 1842, initially designed by Robert Mills and later expanded by Thomas U. Walter and others. The impressive 15th Street colonnade was perhaps intended to convey an impression of timeless strength for the building housing the financial activities of the federal government. Mills's south portico (around the far corner) looks down the long sweep of Pennsylvania Avenue toward Thomas U. Walter's cast iron Capitol dome. The old State Department building at the right was soon demolished to allow completion of the north facade.