Between 1990 and 1992, archaeological excavations conducted underneath the ancient cellars of the Ambrosiana brought to light a portion of the pavement of the ancient Roman forum, the heart of Mediolanum's political, economic and religious life.
The curia (meeting place of the local Senate), the basilica (where justice was administered), the Capitolium (the temple dedicated to the Capitoline triad of Jupiter, Juno and Minerva) and the tabernae (shops, craft workshops and taverns).
These are slabs of Verona stone of varying sizes, arranged oriented north-south or east-west, apparently with no regular pattern. In the part of the excavations that can be visited today, below the current Sala Fagnani and Sala Custodi of the Biblioteca Ambrosiana, there are the remains of a canal that drained the water shed from the porticoes on the long sides of the Forum, which must have measured some 55 x 166 meters.
The construction of the new religious pole of the city, the group of buildings connected with the Episcopal see in the current area of Piazza Duomo, led to the gradual decline of the Forum. The privatisation of public land and the transfer to the bishop of extensive state property led to the area of the Forum gradually being occupied by religious buildings.
We have reliable information from 1030 about the church of the Santissima Trinità, dedicated to the Holy Sepulchre in 1099 on the occasion of the first Crusade. The crypt of the church preserves the original pavement in slabs of Verona stone, probably scavenged from the Roman paving of the forum and reused.