The interior is based on a Greek cross, with each arm divided into three naves with a dome of its own as well as the main dome above the crossing. The dome above the crossing and the western dome are bigger than the other three. This is based on Constantine's Church of the Holy Apostles in Constantinople. The marble floor (12th century, but underwent many restorations) is entirely tessellated in geometric patterns and animal designs. One particular panel in the pavement shows two cocks carrying a trussed-up fox, has been interpreted politically by some, as a reference to the French conquest of Milan in the Italian Wars. Others see it as a sacred symbol of the faithful wish for immortality, with the victory of the cock and "analogous to the hope of resurrection, the victory of the soul over death".The techniques used were opus sectile and opus tessellatum. The lower register of walls and pillars is completely covered with polychrome marble slabs. The transition between the lower and the upper register is delimited all around the basilica by passageways which largely substituted the former galleries.