The Cannon House Office Building was designed to enrich the Capitol not only in space but in appearance. Part of the larger project of beautifying and rationalizing the development of Washington, D.C., the new office building was an initial step in creating an enclave of marble edifices on Capitol Hill. A harmonious, unified complex surrounding the splendid Capitol was to take the place of the slapdash neighborhood of saloons, shops, and hotels.
The prominent architectural firm Carrère and Hastings planned the new office in the symmetrical, sculptural, and stately Beaux-Arts style, a look that complemented but did not compete with the Capitol. The building is clad in marble and limestone, with 34 columns facing the Capitol. Pilasters of the same height line the west side of the building, whereas the east and south sides, which are not visible from the Capitol or from busy streets, are unadorned. Originally, there were 397 individual offices, and 14 committee rooms. For added convenience, the new building was—and still is—connected to the Capitol by an underground tunnel.