apses cut out of the front: one of these apses would have contained a statue of Agrippa, the other of Augustus. And Romans passing between them (through the great bronze entrance doors that still survive) would marvel at how self-effacing was their Emperor-architect. [Illustration: FIG. 11.10 Rome, Pantheon. (G. Lugli, _Mon. Ant._, 3, fac. p. 126)] [Illustration: FIG. 11.11 Rome, Pantheon, interior, 19th-century reconstruction, drawing by fellows of French Academy in Rome.] The interior (Fig. 11.11) carries forward that liberation of religious architecture from the Greek tyranny of the rectangular box, which can only come about through the use of poured concrete, and which we saw first in the Sanctuary of Fortune at Praeneste. Here Hadrian plays with geometrical abstractions, as in the Teatro Marittimo. The game is to describe a sphere in a cylinder: if the curve of the dome were projected beyond the point where it meets the vertical walls of the drum, the bottom of the curve would be just tangent with the floor. The very pavement, with its alternation of squares and circles, plays up the geometrical _jeu d’esprit_. (Beneath this pavement lies the simple rectangular plan of Agrippa’s temple.) Furthermore, both the plan and the interior view show that the walls of the drum are not solid, and that they continue the architect’s vast toying with geometrical concepts. The walls are lightened with niches (for statues; one, of Venus, wore Cleopatra’s pearls in her ears). The niches are alternately rectangular and curved; the result is that the hemispherical cupola is supported not on a solid wall but on eight huge piers. In order to reduce the bearing weight of the superstructure upon the niches, into the concrete fabric above the apertures were built, concealed by polychrome marble revetment, elaborate brick relieving arches, which run as barrel vaults right through the walls. The cupola itself is designed with sunken stepped coffers, to lighten it, and to exaggerate the perspective, and to play yet again with the alternation of curve and straight line. The concrete of the cupola, which is thinner toward the top, is made with pumice, the lightest material available. But in spite of the pains taken to lighten the enormous mass, the piers gave under the weight of the cupola, and external buttresses proved necessary (see plan, Fig. 11.10), which spoiled the exterior effect. Hadrian is an amateur to the end; his vaults do not hold, his cupolas need bracing, his foundations give--and yet the essence of his designs has lasted forever.