[34] _Op. cit._, vol. 1, p. 201.
[35] _Op. cit._, vol. 1, p. 201.
[36] Vasari, _op. cit._, vol. 4, p. 152, and Milizia, vol. 1, p. 214.
[37] Figures 21 and 22 are taken from Serlio, _D’Architettura_, book 3, Venice, 1560, pp. 25 and 40.
[38] _Op. cit._, vol. 7, p. 163.
[39] Serlio, the architect (a younger contemporary of Bramante), _op. cit._, p. 33, tells us that Bramante, at his death, left no perfect model of the whole edifice, and that several ingenious persons endeavoured to carry out the design, among whom were Raphael and Peruzzi, whose plans he reproduces. That ascribed to Raphael has a long nave, while that said to be by Peruzzi has the form of the Greek cross with round apses and a square tower in each external angle. The whole question of Bramante’s scheme, and of the successive transformations to which the design for the edifice was subjected before its final completion, is fully discussed in the work of Baron H. von Geymüller, _Die ursprünglichen Entwürfe für Sanct Peter in Rom_, Wien and Paris, 1875–1880.
[40] _Op. cit._, bk. 3, p. 37.
[41] Serlio does not state on what authority this illustration is based, but there appears no reason to question its correctness. Its authenticity is discussed by Baron von Geymüller (_op. cit._, p. 240 _et seq._), who accepts it as genuine.
[42] The alterations that have been made at different times since the original completion of this interior are of no concern here. The arrangement was practically the same in Bramante’s time as it is now.
[43] Some writers have supposed (cf. Middleton, _Ancient Rome_, Edinburgh, 1885, pp. 338–339) that the dome of the Pantheon is entirely of concrete, and without thrusts. We have no means of knowing its exact internal character, but there is reason to believe that it has some sort of an embedded skeleton of ribs and arches, with concrete filling the intervals. But if it were wholly of concrete, as Middleton affirms, it would not be safe without abutment; for, even supposing that a concrete vault may be entirely free from thrust in a state of integrity, there is always a chance of ruptures arising from unequal settlement, which might at once create powerful thrusts. However this may be, the fact is that the builders of the Pantheon took care to fortify it with enormous abutment, which would seem to show that they did not consider it free from thrust.