The Piccolomini Altarpiece is an architectural and sculptural altarpiece in the left-nave of Siena Cathedral, commissioned by cardinalFrancesco Todeschini Piccolomini. It was built between 1481 and 1485 by Andrea Bregno in Carrara marble, with additions in the following decades – these included four niche sculptures produced between 1501 and 1504 by Michelangelo of saints Peter, Augustine (later resculpted as Saint Pius), Paul and Gregory.