Dedicated to St John the Baptist, the Baptistery was probably erected on the remains of a Roman villa or thermal baths and is an important example of 5th century Paleochristian architecture.
It is the oldest religious building in Switzerland to have survived fully preserved and was entirely renovated in 1953-1955 by the architect Ferdinando Reggiori.
The church has a square plan with an apse on the eastern side. The octagonal shaped interior has several rectangular and semicircular recesses. At the centre stands the Romanesque baptismal font: a round monolith of Serizzo granite built on top of the older, octagonal font recessed into the ground. The floor is composed of black and white marble tiles in geometrical inlays. The recesses bear precious Romanesque and late Romanesque frescoes depicting the life of Jesus from the Nativity to Crucifixion, as well as a fresco of the Last Judgment. Inside the apse, traces can be seen of a fresco dedicated to the hermit and miracle worker Blessed Manfredo Settàla, who died in 1217 and is still today commemorated in the region.