The Rotonda di San Lorenzo is the most ancient church in Mantua. It is now sunk below the level of the Piazza della Erbe. It probably stands on the site of a Roman temple that was dedicated to the goddess Venus.
It was built during the reign of the Canossa family in the late 11th century. Inspired by the Holy Sepulchre church in Jerusalem and dedicated to the martyr St. Lawrence, it has a central plan and has maintained ancient features like the matronaeum (loggia for female faithful) and frescoes of the Byzantine school from the 11th-12th century. Another fresco fragment in the apse, portraying the Martyrdom of St. Lawrence, dates to the 15th century. The construction, according to the Lombard tradition, is in bricks, but has two columns and other details in marble, coming from ancient edifices.
Deconsecrated, it was used for dwellings, shops and stores, and at the beginning of the 20th century it was covered by other edifices. Later, it was restored and the external additions removed.
References:Sigmaringen Castle was first mentioned in the year 1077 in the chronicles of Petershausen monastery. The oldest parts of the castle are concealed beneath the alterations made during the 17th and the 19th centuries. The secret of the earliest settlement built on this defendable rock will never be fully revealed: large-scale excavation work would be necessary, which the extensive land development renders impossible. Judging from the many Roman remains unearthed in the area around Sigmaringen, the 12th century keep known as the 'Roman Tower' could be traced back to a Roman predecessor.
The castle remains that have been preserved (gate, great hall and keep) date back to the Staufer period around 1200. The castle remains were integrated into subsequent buildings. The foundations of the castle buildings are to a large extent identical to the surrounding castle wall.
These remains give us a good idea of how the castle might have looked during the 12th century.