The building has the classic plan of a Roman church, with the main nave and side nave, the apse and the dome built at the intersection of the main nave with the transept, in the form of a Latin cross with unequal arms. The entrance is made by three Roman portals, separated by niches of blind masonry, finished by a horizontal development of semicircular Roman arches, the arch that continues on the side walls of the monument. Horizontal strings of wall construction elements accentuate its decorativism, monumentality, and stability. The facade rises on 5 levels. It is massive on the ground floor and decorated on the next 4 levels with repeated, overlapping rows of columns. The side walls, on 3 levels, have small openings through the windows framed by semicircular arches, and the same type of ornaments can be found at the drum at the base of the dome. It is built out of bright white marble, highlighted and accentuated by the intensity and infinity of the blue sky that reflects the blue of the nearby sea water. This is where Galileo was baptized, in the baptistry of the Cathedral of Pisa, and also where he, while studying at the University of Pisa, formulated the "isochronism of the pendulum" ("law of the pendulum") watching the oscillations of a lamp in the Cathedral of Pisa.