Originally Posted by Matchlock
Another of the extremely rare instances in period artwork where a spanning belt and hook are illustrated; this, from a Swabian painting of ca. 1430-40, Bavarian National Museum (BNM), inv.no. MA 3395, is probably the earliest!
Quite the contrary, spanning hooks are often depicted in medieval artwork, I needed only a minute to find an earlier one. St. Stephan South-Tyrol c.1400-1410.
Pleas note the kink in the trigger lever, with an angle > 90 degrees.
This is a clear indication for early crossbows of the 14th century.