Besides the works of the 14th-century masters Duccio, Pietro, and Ambrogio Lorenzetti, as well as Simone Martini, see Siena's 16th-century Mannerists, painting at a time when the Renaissance teetered on the brink of effete Beccafei's dreamy Birth of Mary and a highly decorative Christ at the Column by Sodoma.
You should check out Siena's 16th-century Mannerist group of painters.