Being very old, the Baptistery of the Cathedral has an octagonal structure, whose harmony of parts is the result of the application of the golden section. But why an octagonal structure? Seven is the perfect number, but eight, or seven + 1, expresses absolute perfection, because not only is it the symbol of infinity turned upside down and therefore of eternity, but it also represents the new creation. While God's old creation took place in seven days, the new creation would in fact start from the eighth, which in this case is represented by the baptismal rebirth.