The purpose of the Carnegie Institution of Washington, founded in 1902, was “to discover the exceptional man and to promote original research.” From the beginning, discussions focused on the way in which the inherent dichotomy between these functions might be expressed architecturally. The difficulty was reconciling in a single structure the visual symbol of such an exalted endeavor and yet providing such amenities as scientific laboratories. Carrère and Hastings of New York were selected as the architects. Their design for a three-story pavilion dominated by an unpedimented hexastyle Ionic portico on the exterior and monumental rotunda behind it was based on late eighteenth-century Parisian models. Separation of office functions from the public reception areas (which included a hall on the main axis behind the rotunda) is clearly articulated on the exterior by the interpenetration of two volumes, the subordinate single-bay wings dominated by the overscaled, balus-traded portico. The limestone walls are treated with great restraint, with three different shallow quoin patterns demarcating the basement level, enframing the wings, and articulating the wall behind the slender Ionic columns.
On the interior, the 37-foot rotunda continues the exterior's Renaissance-inspired vocabulary in its interpenetration of ancillary spaces at two levels, alternation of in antis framed openings with protruding double-Corinthian-column piers that frame richly ornamented shell niches. The elegance of the walls is complemented by the radiating floor pattern in gray granite, white marble, and red and green variegated marbles. The walls are cast stone to imitate ashlar masonry, and the wooden columns are painted to resemble marble. The addition to the north by Delano and Aldrich (1938) provided an alternate business entrance on P Street, thus making the main portico a ceremonial entrance.