On the vertical arm is the story of the Virgin with the Coronation, the Assumption and the Burial. On the horizontal arm, from the left, are the patron saints Bartholomew, Ansano, Crescenzio and Savino.
Nothing is known about the identity of the master glazier who undertook the job.
However, it may be safely asserted that it was Duccio who made the preparatory drawings. In September 1287 the Comune of Siena entrusted the administrator of the Opera del Duomo with the task of arranging for the execution of a stained-glass window, and undertook to supply the necessary money for expenses. This agreement was evidently not kept because in May of the following year the Comune threatened to fine the camerlengo, or papal treasurer, and the administrators of the Biccherna if they did not reimburse the workman with the money for the purchase of the glass. At that particular moment in history, the only Sienese painter able to perform such an exacting task, and whose artistic ability had already been proved, was Duccio. A stylistic analysis further supports this conclusion.