Siena Cathedral
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. He substantially changed the design and construction of the building, increasing the similarity of the building to Siena Cathedral. The architecture of both buildings sometimes is classified as a substyle of Gothic architecture: Siennese Gothic style.