 The cathedral was initially designed as a Romanesque basilica with a nave and two side aisles.However, when Giovanni di Uguccione succeeded Fra Bevignate, the design was transformed into Italian Gothic forms.Construction continued slowly until, in 1309, the Sienese sculptor and architect Lorenzo Maitani ("universalis caput magister") was commissioned to work on the church and solve several issues concerning the load-bearing capabilities of the building, especially of the choir.