The church of San Calimero has an elegant and somber linear style. Over the centuries architects have intervened on the structure many times and, nowadays, what we admire is mainly the result of the main transformation that took place at the end of the XIX century, fruit of the work of the architect Angelo Colla who aimed to restore the original Romanesque purity.The interior is a single rectangular shaped nave with a roof that was originally trussed whilst the division, in spans covered by oblong vaults, belongs to a successive phase that cannot be precisely determined due to all the reconstructions of the building.
Traces still remain of the Roman phase of the building; they have not been cancelled by the frequent modifications and the restorations of successive eras. These are on the southern side of the apse, opened by three wide curved windows characterized by the presence of the upper arches.The first major restoration took place in the seventeenth century when the work was entrusted to the architect Francesco Maria Richini. The eighteenth century left its imprint with the rich marble decorations offered by the Confraternity of the Blessed Sacrament and in the San Michele oratory which, nowadays, is used as a sacristy. The main altar, with elegant neoclassic lines, is from the beginning of the nineteenth century.The church is dedicated to San Calimero a nobleman who, after a voyage to Rome, was consecrated into the priesthood.
He was a contemporary of S. Castriziano and he succeeded him as bishop. History declares that San Calimero was a martyr as he was thrown to his death in a well by Pagans.The location in which the Basilica was erected was formerly a burial ground outside the walls of the city: still today on the walls on the right side of the church there are some Pagan and Christian grave stones from the ancient necropolis. The tale handed down through the centuries says that San Calimero was buried here and that the church was dedicated to him, probably existing from the times of Bishop Ambrogio and most likely it was a Basilica cemetery at least until the XIII century. It seems that the Basilica was built, in the V century, on the remains of a temple dedicated to Apollo, as stated in a chronicle from the IX-X centuries.