Baptistery of San Giovanni ad Fontes, Early medieval baptistery in Lomello, Italy

The Baptistery of San Giovanni ad Fontes is a brick baptistery beside the basilica of Santa Maria Maggiore in Lomello, 13 m high and 16 m long on the east-west axis. Its exterior reads as a cross, while the interior centres on an octagon carrying an octagonal dome, a later 10th-century addition built with plainer materials. The interior is fully plastered and entered through two portals, the main one to the west.

This structure was founded during the early medieval period, with brickwork originating from the 5th to 6th centuries forming part of the original construction. A dome was added in a later phase, marking an evolution in the building's architectural development.

The structure displays hallmarks of Lombard design with its brick walls and unusual octagonal footprint. It served as part of an early medieval sacred site where believers were baptized, a spiritual role that the space still reflects today.

The baptistery stands beside the basilica of Santa Maria Maggiore and is reached through two portals, the main one on the west side. The interior is entirely plastered and the central octagon rises under the dome. The building is 13 m high and 16 m long on the east-west axis, so allow time to walk around the exterior brickwork as well.

The hexagonal baptismal font dates to the 7th–8th centuries and was likely inspired by eastern models reaching Lombardy through the Patriarchate of Aquileia. A small painted basin for aspersion was later added inside the immersion pool.