The Baptistery was built in 1516 on the site of an older church dedicated to St. Martin.
After the demolition of the old Baptistery in 1555, when the square was enlarged after the construction of the new cathedral, it took both the title and the function.
The 1873 earthquake destroyed the nearby little church of St. Andrew, from which comes the XIV century painting of the Madonna delle Grazie, while its collection of little wooden votive paintings from XV to XIX centuries is now shown in the City Museum.
Inside, on top of the baptismal basin, there is a little statue of St. John the Baptist by Andrea Brustolon (1662-1732).
