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:
The Externsteine (Extern stones) is a distinctive sandstone rock formation located in the Teutoburg Forest, near the town of Horn-Bad Meinberg. The formation is a tor consisting of several tall, narrow columns of rock which rise abruptly from the surrounding wooded hills. Archaeological excavations have yielded some Upper Paleolithic stone tools dating to about 10,700 BC from 9,600 BC.
In a popular tradition going back to an idea proposed to Hermann Hamelmann in 1564, the Externsteine are identified as a sacred site of the pagan Saxons, and the location of the Irminsul (sacral pillar-like object in German paganism) idol reportedly destroyed by Charlemagne; there is however no archaeological evidence that would confirm the site's use during the relevant period.
The stones were used as the site of a hermitage in the Middle Ages, and by at least the high medieval period were the site of a Christian chapel. The Externsteine relief is a medieval depiction of the Descent from the Cross. It remains controversial whether the site was already used for Christian worship in the 8th to early 10th centuries.
The Externsteine gained prominence when Völkisch and nationalistic scholars took an interest in the late 19th and early 20th centuries. This interest peaked under the Nazi regime, when the Externsteine became a focus of nazi propaganda. Today, they remain a popular tourist destination and also continue to attract Neo-Pagans and Neo-Nazis.