Although Walter had envisioned plain-colored walls hung with oil paintings, Captain Montgomery C. Meigs, Superintendent of Construction, directed Brumidi to carry out an elaborate decorative scheme based on Raphael's Loggia in the Vatican.
Brumidi's classical training in Rome gave him a thorough understanding of ancient Roman, Renaissance, and Baroque styles, symbols, and techniques of wall painting.
An English artist, James Leslie, painted parts of the walls and ceilings of the corridors, including some of the birds and animals copied from specimens borrowed from the Smithsonian Institution.
Brumidi created the portraits and historical or allegorical scenes in the semicircular lunettes over the doorways in the difficult true fresco technique.
On the intricately decorated walls can be seen an amazing variety of classical gods and goddesses; birds of a hundred different species; rodents, including chipmunks, squirrels, and mice; insects and reptiles; and flowers and fruits.
Along the walls, Brumidi painted monochrome profile portraits of famous early Americans (John Hancock, Francis Hopkinson, Robert Livingston, Roger Sherman, John Jay, Charles Thomson, Charles Carroll of Carrollton, and Robert Morris) set in medallions to resemble reliefs carved in stone.
Over S-124, which was then used by the Senate Committee on Territories, Brumidi painted The Cession of Louisiana (45k), depicting the meeting of Robert Livingston, James Monroe, and the François Barbé-Marbois in 1803.
At the east end of the north corridor, over S-118, then occupied by the Senate Committee on Foreign Relations, Brumidi painted The Signing of the First Treaty of Peace with Great Britain (44k).
For the area known as the Patent Corridor, Brumidi created frescoed lunettes with three important inventors: John Fitch (47k) (working on his steamboat model), Benjamin Franklin (40k), and Robert Fulton (18k).
The most recent addition to the corridor is the scene depicting the Space Shuttle Challenger mission crew, painted by Charles Schmidt in 1987.
Aside from constant repainting, the walls were protected with varnish, which discolors over time, so that gradually the backgrounds turned from creamy white to yellow and the borders from sandstone color to murky green.
In some cases, these "restorers" proudly signed and dated their work, which included changing costumes and colors and adding their own details over Brumidi's composition.
Unstable plaster was consolidated to make it firm, layers of overpaint were painstakingly removed, mainly with sharp scalpels, and missing details were inpainted.
Although a clear protective coating is being applied to the restored murals, they are extremely vulnerable to damage, and care must be taken to make sure that they are not touched or bumped.
The ornate bronze railing of the stairways used by senators at either end of the north corridor are composed of cherubs, eagles, and deer entwined in leafy rinceaux that echo the wall decoration.
The encaustic tile, made of inlaid colored clays, was chosen for its beauty, durability, and rich design, which complement the painted decoration of the corridors.