For Roland in particular, I have found that the collection of woodcuts from
Der Weisskunig to be especially helpful for visualizing material for Gerhard.
It's later than our current period by a few decades at the least, and it is specifically German, but it provides a wealth of arms and armor illustrations from the period as well as illustrations depicting warfare in general at the time, i.e early artillery emplacements alongside well armored infantry formations with pole arms, cavalry, executions, etc.
I'll link it here if it would be of any help.
https://commons.m.wikimedia.or...ts_by_Hans_Burgkmair