Yesterday was and is the traditional day of the Feast of the Chair of St Peter at Rome, and said to be the day on which the Prince of the Apostles first presided liturgically in Rome. In the Novus Ordo this feast is now celebrated as the Chair of Peter on February 22nd, the traditional feast of the Chsir of St Peter at Antioch.
No doubt with this in mind The Liturgical Arts Journal website has an interesting article about the Constantinian basilica of St Peter with a series of reconstructions of the building. This was the building which along with the Lateran basilica as well as other Roman churches hosted Papal liturgies for over a millennium as wee, from that of Charlemagne in 800 Imperial coronations.
The post also has a link to an earlier article on the site about the remains of the original tomb of St Peter beneath the present High Altar and baldacchino of Pope Urban VIII and the early development of what became the Vatican basilica. The two articles are accompanied by excellent illustrations and can be accessed at Reconstructions of the Interior of St. Peter's Basilica as Built by the Emperor Constantine