by a cylindric tambour pierced with large rectangular windows. The cube is finished with a stone cornice while the tambour is decorated with a brick modillion trim. The low conical roof is covered with tiles but originally it was leaded. The dome is crowned by a small stone lanternino which has niches instead of windows between Tuscan pilasters and its base is decorated with four scrolls. This miniature round temple is topped with the symbols of the Chigi family, the mountains and the star with a cross. The exterior is practically invisible due to the location of the chapel behind the city wall, the Porta del Popolo and the main body of the basilica. Its simplicity and severe appearance was based on the reception of ancient Roman central-plan buildings for example the Temple of Minerva Medica. Interior Raphael's centralized plan was inspired by the designs of Bramante for the new St. Peter's Basilica. Another source of inspiration was the Pantheon with its dome, marble revetments and Corinthian pilasters. The simple cube is surmounted by a hemispherical dome resting on a high drum which is penetrated by a row of windows that allow light into the chapel. The trapezoidal pendentives were the characteristics of Bramante but the whole conception of space, which requires the viewer to look at from several points of view to capture its splendor, is new and unique. The side walls are made up of round-headed arches, of which only the entrance arch is open, the others are blind; they are alternated with canted corners in which shell-headed niches are framed between Corinthian pilasters. The subtle use of coloured marbles emphasizes the individual elements of the classical architecture. The portal of the chapel is a Renaissance reinterpretation of the entrance bay of the Pantheon. It has a monumental effect with double transverse arches resting on huge Corinthian pilasters. The marble pilasters have cable-fluted shafts and beautifully carved, vivacious capitals which were practically copied from the much admired classical model. Raphael had studied the ancient building and created a precise architectural drawing of the entrance which is now preserved in the Uffizi. The entablature and the cornice is decorated with egg-and-dart, bead-and-reel and flower-patterned enrichments. The pilasters are of polished white Carrara marble with faint grey veins while the capitals are of unpolished pure white Carrara marble. The surfaces between the pilasters are covered with a coloured marble revetment,