Gianfrancesco Penni
Born in Florence to a family of weavers, Penni entered Raphael's workshop very early in his life, and collaborated with him on several works, including the famous Rooms of the Vatican Palace, as well as the frescoes of Villa Farnesina, both in Rome. Heinrich Wölfflin and some other writers credited him with the entire execution of the Raphael Cartoons, with Raphael only creating the initial design, though more recent writers believe Raphael did much of the work himself.
Hexadecagon
In the early 16th century, Raphael was the first to construct a perspective image of a regular hexadecagon: the tower in his painting "The Marriage of the Virgin" has 16 sides, elaborating on an eight-sided tower in a previous painting by Pietro Perugino.
Hexadecagrams (16-sided star polygons) are included in the Girih patterns in the Alhambra.