The enigmas of the tympanum of Moissac :

At the tympanum of Moissac, in the beginning of the 12th century, a sculptor illustrated a moment of Saint Jean's Apocalypse.
Thus he sculpted in the rock, 24 ancient men holding a vase of perfume and a musical instrument.

Why do these instruments "rebeckes" have baroque sound holes shape?
Why are the bridges centred like on violins?
Why is the fingerboard already present?
Why so modern peg of pins?