Actually, see if there are any remains left of the Baths of Constantine. The baths were just south of the where the statues of Castor and Pollox at the Quirinali Palace are today. There might be some remains (or maybe a plaque on some wall) within one of the villa gardens on the site now. Likewise, see if you can find that big "bouncing" ball that was originally atop the obelisk of St. Peter's before it (the obelisk) was moved to the piazza. I think the ball is in one of the museum at the Campidoglio.
Re: FW Evolutionary theory and architecture
Aside from strictly religious (temple and church) architecture, the case can be made that classical Roman architecture, in general, reached its climax during the reign of Maxentius, and ended 28 October 312, when Maxentius lost his life in battle with Constantine at the Milvian Bridge--Maxentius became (usurpative) emperor of Italy and North Africa 28 October 306, and Constantine attributes his Christian conversion to events that occurred the eve of 28 October 312. The architecture built in Rome under Maxentius is of the utmost refinement, e.g., the Circus of Maxentius manifests the most precisely designed of all Roman circuses. [Incidentally, the Circus of Maxentius plays a key role in the manifestation of two Ichnographia Campus Martius.] Records indicate that it may have been only a month after Constantine's triumph at the Milvian Bridge that the first Christian Basilica in Rome, first named after Constantine and today St. John Lateran, began construction. The architecture of Rome executed under Constantine (312-330) further includes (at least), St. Peter's at the Vatican, separate Basilicas of St. Lawrence, Agnes, and Peter et Marcellinus, Santa Croce in Gerusalemme (which is all that remains today of Elegabalus' Sessorian Palace, where Helena took up subsequent residence in Rome), the Arch of Constantine (which reused pieces of the Arch of Trajan), the Baths of Constantine, the Baths of Helena, and the Mausoleum of Helena (whose ruins exhibit construction very similar to the ruins of the great Constantinian Bath of Treves (Trier, 306-312), which were the largest Roman Baths outside Rome).