The Constantine (or Lateran) Baptistery, also called San Giovanni in Fonte or San Giovanni in Onda, was built with ancient materials no later than the age of Sixtus III (432-440). Its octagonal structure became the model for many baptistries throughout the West. It traditionally recalls the eighth day, symbol of the risen Christ. It is precisely baptism that signifies the first step in this day without end. The architectural forms closest to the original ones were obtained from the excavations, such as the plan, the course of the perimeter wall and the position of the reinforcement pillars.