The monument is a diminutive adaptation, in simplified form, of a local mediæval type of building of which San Vitale of Ravenna appears to have been the original example, and San Lorenzo of Milan an offshoot. There are points of similarity between the sacristy of San Satiro and the church of the Consolazione of Todi (Fig. 36, p. 76) that go far to determine their common authorship. The superimposed pilasters broken into the angles of a polygon, the niches in the lower bays, and the ribs on the surfaces of the vault rising from the pilasters[105] are similar in both. A curious domed structure of the early Renaissance in Milan is the east end of the church of Santa Maria delle Grazie. The dome is hemispherical, and is raised on a drum resting on pendentives over a square area. The most noticeable part of the composition is the exterior, which completely masks the inside. The drum (Fig. 80) is a polygon of sixteen sides, and is in two stages, the lower one of which is solid, and rises above the springing of the vault, while the upper stage, in the form of an open arcaded gallery, with an attic in retreat, reaches far above the haunch of the dome which is covered with a low-pitched roof of timber crowned with a lantern. The lower stage has an order of pilasters with a nondescript entablature, having an enormously high frieze ornamented with an engaged balustrade. A pair of square-headed windows with mullions, surmounted with pediments, opens through each face of the polygon, except the four which fall over the piers of the interior. Against each of these sides a turret rises, forming an abutment. A panelled podium crowns the entablature of this lower stage, and upon it the shafted arcade of the top story rests. The north and south sides of the square beneath have each a low apse, while on the east is a rectangular choir with an apse like the other two. The architectural treatment of this exterior is not expressive of the inside. The square parts are divided into four stages answering to nothing within, and the lower three of these stages are carried around the apses. The wall surfaces are broken into rectangular panellings by mouldings and pilasters, every alternate pilaster in the third stage having a tapering ornamental member, like the window shafts of the Certosa of Pavia, worked in relief on its face; and the panels are adorned with disks and medallions. Like most of the early Renaissance architecture of Milan, this building is entirely of brick with ornaments of terra-cotta. [Illustration: FIG. 80.--Santa Maria delle Grazie.]