There is always debate and controversy over the "form" of a tool as it passes through history. This stained glass window is from the Sainte Chapelle in Paris France. Built by/for King Louis IX to commemorate his heading off to crusade (the 7th Crusade) and to house the very valuable relics from the Passion he'd managed to purchase from Byzantium.
The window was created around 1240 - 1250 AD. It shows Christ carrying the cross through Jerusalem and a man standing by, hammer in hand.
The hammer obviously has a claw, not unlike a modern hammer. Almost looks like an Estwing brand.
I find that interesting. . .
We have to be careful about what we think we know about the past. Those old boys were pretty smart.
Ratione et Passionis