White marble statue, depicting the prophet Isaiah, sculpted by Bernardo Ciuffagni in 1424 and coming from the medieval facade of the Cathedral. When the facade was dismantled in 1587, the statue was placed inside, in the current marble aedicule designed by Bartolomeo Ammannati. The prophet is larger than life, is standing and is rapresented as an elderly man, with short hair and a long flowing beard; he turns his gaze to the left with a frown and serious expression. He wears old-fashioned sandals and is dressed in an abundant tunic. In one hand he holds an open scroll, close to his chest, and with the other hand holds a book closed tight to his side. Ciuffagni's style still close to the late Gothic tradition (especially in the linearity of the drapery) but we recognize an opening to the "Renaissance" of Donatello in the naturalism of the face.

The iconographic subject is appropriate both for the facade of the Cathedral and for the bell tower (to which according to some it was destinated): Isaiah is one of the four major biblical prophets, author of the book of the Old Testament theat bears his name. Christian theology has interpreted many passages of his prophecies as references to Christ and the apocryphal Christian tradition remembers him as a martyr. His prophetic work is a stern warning to Jerusalem and a constant warning to rely on God in preparation for imminent threats; this explains the hard expression of the face and the decisive gait of the pose with which he is depicted. Therefore he is presented as example of moral strength and Faith, and this artwork had the meaning of reference to piety and virtue.