The " small rhombicuboctahedron " is bounded by 12 pentagonal, 8 triangular and 6 square faces; the " great rhombicuboctahedra " by 12 decagonal, 8 triangular and 6 square faces.
It is circular internally and decagonal externally, in two storeys, built of marble blocks, and surmounted by an enormous monolith, brought from the quarries of Istria and weighing more than 300 tons.
There remain a fragment of the south wing of the transept, two sides of the decagonal chapter-house (1282) and the beautiful west gate-house, Early Perpendicular (1332-1388), with an oriel window on the east.