I just stumbled across this very interesting video, which gives a virtual reconstruction of the Constantinian Basilica of St Peter in the Vatican, as it would have been roughly at the end of the first millenium. What we see here is sort of a “bare-bones” version of the church, which shows very little of the decorations or the innumerable side-chapels and altars (over 120 of them, 27 dedicated to the Virgin Mary alone!)By the beginning of the 16th century, when the church was close to twelve centuries old, parts of it were collapsing under the weight of the ceiling, and the north wall had a stretch of about half its full length which was sagging about a meter off the perpendicular. It was therefore torn down in various stages, and after a long series of fits and starts, rebuilt as the church which we know today by the genius of Michelangelo and his successors. In the year 1590, a canon of the church, Tiberio Alfarano, published this famous plan which shows where everything was in the ancient basilica. (Click to enlarge.)