The Parthenon is considered by authors such as John Julius Norwich "the most perfect Doric temple ever built". Its elaborate architectural refinements include "a subtle correspondence between the curvature of the stylobate, the taper of the naos walls and the "entasis" of the columns". "Entasis" refers to the subtle diminution in diameter of the columns as they rise. The stylobate is the platform on which the columns stand. As in other classical Greek temples, the platform has a slight parabolic upward curvature to shed rainwater and reinforce the building against earthquakes. The columns might therefore be supposed to lean outwards, but they actually lean slightly inwards so that if they carried on, they would meet about a kilometre and a half above the centre of the building; since they are all the same height, the curvature of the outer stylobate edge is transmitted to the architrave and roof above: "all follow the rule of being built to delicate curves".