Arnolfo di Cambio
The front side was done in his workshop, partially by Nicola Pisano himself but mostly by his assistant Lapo di Ricevuto. and another famous sculptor Arnolfo di Cambio. The Dominican brother fra Guglielmo da Pisa (who also designed in 1270 a pulpit in San Giovanni Fuorcivitas in Pistoia) made a small contribution. According to "Gnudi" (see ref.) an anonymous Fifth Master was also involved. A collaboration of several sculptors on such a large commission was normal practice in medieval sculpture.