This and other fragments in the Collection are from a large fresco (now transferred to canvas) of the 'Fall of Lucifer' which was painted for the Compagnia di Sant' Angelo or S. Michele Arcangelo in Arezzo, Italy.
The scene shows Saint Michael and other angels fighting a war in heaven. The battle took place before God who was originally shown enthroned above, while Lucifer's agents plunge to earth below. The story is from the New Testament (Revelation 12: 7-9).
According to the painter and biographer Giorgio Vasari (1511 - 1574), Spinello made the figure of Lucifer so horrible that it gave him bad dreams and he died soon after.
This fragment of Saint Michael was not cut horizontally from the fresco; the right-hand end is considerably higher than the left-hand end.