Many baptisteries are octagonal in shape, including the one in Pistoia, dedicated to Saint Giovanni in Corte and dating back to the second half of the 14th century.

Most experts believe that the eight-side polygonal floor plan of these holy structures, once built near churches, was inspired by the Bishop of Milan, Saint Ambrose, who promoted the construction of the Baptistery of San Giovanni alle Fonti, in Milan, next to the ancient Basilica dedicated to the virgin martyr Saint Tecla, in what now is Piazza Duomo.