The round window in the apse, an outstanding masterpiece made between 1287 and 1289-90 on a drawing by Duccio di Buoninsegna and currently replaced by a copy, is the first element in the cathedral that captures the visitor’s eye. The three central panels illustrate the Dormition, Assumption, and Coronation of the Virgin, clearly showing the goal of every person’s journey, the Kingdom of Heaven.
In the first panel starting at the bottom, Our Lady is laid in a sarcophagus by two apostles while the others crowd around, accompanied by three angels. In their midst is the figure of Jesus Christ giving His blessing. The scene presents the end of Mary’s time on earth, an episode called the ‘Dormitio Virginis’ and not ‘the Death of the Virgin.’ This is because She, conceived without sin and thus preserved from the corruption of the flesh, does not have to wait for the end of the world, like all other creatures, in order to take part in the bodily redemption, but is taken up into Heaven body and soul.
The central panel shows Her Assumption, the moment when She passes from the earthly condition to the heavenly, in other words when She becomes divine. In the case of the Virgin we use the term assumption because She rises to Heaven by virtue of Her Son, while for Jesus the correct term is ascension because He rises on His own. In the scene, Mary is set into a mandorla surrounded by four angels: this shape, obtained by intersecting two circles, represents the ideal union of heaven and earth. It is a sort of halo destined only to Jesus and the Virgin, the symbol of their divine and human nature, their glory and perfection.
The third frame presents the Virgin being crowned by Jesus; both sit on the same throne, surrounded by angels. Mary is made to participate in Her Son’s glory, fully conformed to Him. She anticipates the destiny common to all the faithful, foreshadowing the definitive spiritual and bodily union of human beings with the glorious Christ, that is to say the final, eternal phase of redemption.
The side panels of the window hold, in the central band, the four Patron Saints of Siena, Ansanus, Crescentius, Sabinus, and Bartholomew (substituted a few years later by Saint Victor). They represent the local Church, placed under Mary’s protection. In the four corners are the Evangelists, each seated on a throne. This placement is not coincidental: they symbolize the Word of God which constitutes the foundation of the Church, reaching the four corners of the earth thanks to its ministry.
The original window, whose restoration was finished in 2003 and since then has been placed for protection in the Museo dell’Opera, is a truly outstanding work, because of both the very high level of quality and its exceptionally well-preserved state, making it one of the earliest examples of stained glass known today. It was the most prestigious commission received by Duccio before the one for the Maestà for the high altar of the cathedral. The artist did not limit his work just to the preparation of the drawing (which was translated into stained glass by one or more master glassmakers), but, as it was possible to observe during the restoration, his hand was certainly responsible for the refined grisaille details painted onto the glass with a brush, which give remarkable effects of light and shadow to the figures.