[54] “Cominciato forsi poco dopo terminata la fabrica.” _Op. cit._, p. 13.
[55] _Ibid._, p. 14.
[56] _Ibid._, p. 15.
[57] _Ibid._, p. 19.
[58] _Op. cit._, vol. 2, pp. 327–328.
[59] It is true that fissures in a properly constructed vault are not necessarily alarming. Any vault may crack from unequal settlement of the supports. Gothic vaults are sometimes slightly ruptured in this way, but they are not thus endangered, because they are effectively buttressed. But fissures in a dome without abutments may be a sign of impending collapse.
[60] _Ibid._, pp. 328–329.
[61] _Ibid._, p. 388.
[62] _Op. cit._, p. 399.
[63] The principal work of Bramante’s immediate successors on the fabric itself appears to have been to strengthen the great piers, which seem to have been built too hastily, and on insecure foundations. Poleni tells that in order to strengthen these foundations, well-holes were dug under them and filled with solid masonry, and that arches were sprung between these sunken piers, consolidating the whole. _Op. cit._, p. 19.