What did the citizens of Rome know about the Empire during medieval times?

A pope made a visit in Ostia (sadly I can't remember who) and was amazed to find buildings with multiple stages there. Most of ancient text where still read in medieval times, the natural history of Pliny the Elder was very well known. I also know that some pagan celebrations were still alive in a more or less christianized form centuries after the forbidding of paganism. The most "pagan" of them were forbidden in the early middle ages like the lupercalia

On a more institutional level, Rome enjoyed some degree of communal autonomy represented by his senate, due to the increased control over the pope, the number of senators would gradually decline until it was reduced to one senator EDIT: it was done earlier than I remembered, in the end of the XIIth century But most of the monuments were transformed into little castles like the triumphal archs of Constantine and Septimus Severus. The biggest (and most iconic) building to have been fortified is the mausoleum of Hadrian wich became the Castel St Angelo. In addition Constantine played a key role in Papal legitimation and its memory was very well known has the founder of the great churches of Rome (mainly St Peter and St John Latran). The statue of Marcus Aurelius on the Capitoline hill (now in the adjacent museum) was kept intact because it was believed to be a statue of Constantine which was displayed near the entrance of St John Latran. Moreover the emperor was the center of the legend of the donation of Constantine where he was supposed to have given to the pope the power in all the western empire, a blatant fraud to assert the hegemony of the pope over the kings in the age of the crusades. Another key sources are hagiographies, the lifes of the saints. As most of the martyrs were killed in the first centuries of christianity, they were romans and some contained details of monuments that completely disappeared today. Even if those stories were not read for the mentions of pagan monuments, the memory of the pagan Rome was kept alive

Finally for the (educated) people of the middle ages, the empire was not at all dead. He continued in the east with the byzantine (who called themselves romans) and in the west after the restauration of Charlemagne. The fourth and last empire of the prophecy of Daniel (before the end of the world) was understood at the time as the roman empire, but as long has there were emperor in the holy roman empire, the world was safe.

edit: spelling and some minor clarifications edit II: I reopened "Rome, l'idée et le mythe: du Moyen Age à nos jours" and found that the reduction of the number of senators to one was made earlier than I thought.