 The encircling peristyle of Bramante and the arcade of Sangallo are reduced to 16 pairs of Corinthian columns, each of high which stand proud of the building, connected by an arch.Visually they appear to buttress each of the ribs, but structurally they are probably quite redundant.The reason for this is that the dome is ovoid in shape, rising steeply as does the dome of Florence Cathedral, and therefore exerting less outward thrust than does a hemispherical dome, such as that of the Pantheon, which, although it is not buttressed, is countered by the downward thrust of heavy masonry which extends above the circling wall.