The Enigmatic Shadow of Sienese Mastery To traverse the hallowed halls of the Collegiata di San Gimignano is to encounter a ghost of the Trecento, an artist whose name, Barna da Siena, lingers in the air like incense in a medieval chapel. Known also as Berna di Siena, this figure remains one of the most tantalizing enigmas in the history of Italian art. While the chronicles of Lorenzo Ghiberti and Giorgio Vasari attempt to pin him to…