Rome is different from Egypt and Greece in how you see ruins. This is a giant generalization, but something I noted in our wanderings. For the most part, ruins in Egypt are outside the major cities; they are areas that are set apart geographically from modern structures. It was probably a combination of not wanting to defile the awesomeness of the ancient structures and the harshness of the desert that kept newer cultures from claiming ancient sites for new cities. Even where cities have grown and now encroach upon the once isolated sites, the ruins are still set apart for the most part. In Greece, there are ruins everywhere, and particularly in Athens, the city surrounds them. You can’t dig in the city without finding the remains of some past time. But the policy in Athens is that if there is some archaeological find on your property it is no longer yours, but now belongs to the state in order to accurately excavate the artifacts. As a result there are islands of ancient monuments throughout the city. The major areas like the Acropolis and agoras are huge islands of ancient structures completely surrounded my modern city. But in Rome it is different.
In Rome you find remodeled ancient structures. There are still the islands of “preserved” and “restored” sites like the Foro Romano/Imperiali, Pantheon, and Colosseum. Preserved meaning the ruins are left pretty much as they were found with some reconstructions of the original materials. Restored means that there is a mixture of the ancient ruins with modern materials mixed in to rebuild the old buildings as they may have been originally. But there are also a huge number of ancient structures that are being used for newer contemporary activities. Some became churches (like the first photo on this page) others museums, fortresses, and even housing. Here are just a few examples.
Caesar Augustus completed the Theatre Marcellus in 11BC. It was one of Rome’s first permanent theaters. The Roman Republic viewed performances as a danger to public morality. Therefore theaters were built of wood to retain a sense of non-permanence; if the show was deemed “improper” the theater could always be burned to the ground! It could seat 15,000 spectators. But by the Middle Ages, long after Rome’s fall, it was converted into a fortress for noble Roman families. In the 16th century it was converted into a palace. I’m not sure of this, but I believe I heard that it later fell into disrepair and became housing for the struggling Jewish community of this ghetto area. Those windows up high weren’t a part of the 16th century palace!
The Mausoleum of Hadrian is another fine example of Rome building upon itself. Rome forbade the building of any tombs within its walls so Emperor Hadrian built his just across the river where it was completed one year after his death in AD 139. His ashes were placed in the burial chamber at the base of this cylindrical structure, as were the ashes of future emperors for the next hundred years. A cypress grove was planted on top of this burial chamber and crowned with a huge central column holding a statue of Hadrian riding his horse-drawn chariot. Around AD 590 a vision of the Archangel Michael appeared above the mausoleum and signaled the end of a plague in the city. It was then converted into a fortified palace and named Castel San Angelo after the angel. During the Dark Ages it was again converted, this time into a fortress/prison. Tunnels later connected it to the Vatican and it became a hideout for the Pope during times of invasion. It is now a museum.
The Baths of Diocletian were constructed in AD 300 and could host 3,000 bathers at a time. Roman baths were a combination gymnasium, restaurant, sauna, pool, meeting area. Aqueducts guiding water into the city from the mountains far away fed these baths. Water was heated and steamed in the caldarium, lukewarm in the tepidarium, and left cold in the frigidarium pools. There was a work-out gym with weights and exercise classes. And there were plenty of places where people could just hang out, discuss politics and seal business deals. These were great places. When barbarians invaded Rome they cut the aqueducts, and the baths ceased to be used. In the 16th century the great central hall of the bath was converted by Michelangelo (not of the Teenage Mutant Ninja Turtle fame) into a church. The exterior looks like the marble-façade-stripped exterior of any ruined structure around Rome, but inside you find a beautifully decorated renaissance church. The Roman vaulted ceiling and the red marble columns are the originals. It’s still used today.
After Rome’s fall many of the old structures were dismantled and used in the building of newer structures. The Baths of Caracalla are a great example. The rich marble façade of these huge baths (1,600 people at a time could bathe here) just south of the Circus Maximus were stripped away and used in the construction or back fill of palaces built in the area at later times. All that is left are the empty shells. But even in its ruined state it was used for opera performances from 1938 to 1993.