It took Ghiberti 21 years to complete these doors. These gilded bronze doors consist of twenty-eight panels, with twenty panels depicting the life of Christ from the New Testament. The eight lower panels show the four evangelists and the Church Fathers Saint Ambrose, Saint Jerome, Saint Gregory and Saint Augustine. The panels are surrounded by a framework of foliage in the door case and gilded busts of prophets and sibyls at the intersections of the panels. Originally installed on the east side, in place of Pisano's doors, they were later moved to the north side. They are described by the art historian Antonio Paolucci as "the most important event in the history of Florentine art in the first quarter of the 15th century".