Sano di Pietro's portrait of Pope Calixtus III , as protector of the city of Siena , commissioned by the Sienese in gratitude for the pope's intervention against Jacopo Piccinino whose breach of the Italian League threatened the peace of the peninsula .
Sano di Pietro's portrait of Pope Calixtus III , as protector of the city of Siena , commissioned by the Sienese in gratitude for the pope's intervention against Jacopo Piccinino whose breach of the Italian League threatened the peace of the peninsula .