Here is a cool series of photographs from the 1850s, when the Department of Treasury’s building on 15th St. was under construction.
A. B. Young (of Boston) Supervising Architect, Treasury Department.
Ground floor of the Treasury extension (Photographed & reduced from a drawing).
Proposed south & west fronts of the Treasury extension Photographed (& reduced) from a drawing – (the west front faces the President’s house).
Construction of the south wing of the Treasury building
U.S. Treasury building, Washington, D.C.
S.W. view of excavations, south Treasury extension (Rear of the present State Department building, on the right of picture).
Source: Library of Congress
We have a couple other great photos of the Treasury Department posted here and here.