Braies
Like most Medieval manuscript illuminations, the mid-13th century Maciejowski Bible depicts scenes from the Old Testament in "modern dress". This aspect of the bible, coupled with its wide ranging collection of utensils, equipment, armour and clothing makes it one of those sources ideally suited to re-enactment needs.
In this Bible, braies - the male undergarments of our period - are depicted in a number of stories: they are worn by hot and hard-working farmhands, they are shown worn by some semi-stripped hanged men, and even King Saul wears a pair.
This is presumably a reflection of the ubiquitousness of these items across the social spectrum. In each case they are carefully and skilfully drawn, and all follow a similar format. It would strongly suggest that the illustrator knew what he was drawing and that he also assumed the audience would recognise them as appropriate and recognisable garments.
One of the clearest views that we have is of this man threshing wheat.