The Cathedral of Siena photographed under warm sunlight the cathedral has the form of a Latin cross with a slightly projecting transept, a dome and a bell tower The dome rises from a hexagonal base with supporting columns The lantern atop the dome was added by Gian Lorenzo Bernini The exterior and interior are constructed of white and greenish-black marble in alternating stripes, with addition of red marble on the faade Black and white are the symbolic colors of Siena, etiologically linked