Bailey was the most common grain in the viking age (in Scandinavia). The Danish word for barley; “byg”- means grown grains. The archaeologists think that crackers of barley flour have been common.
Neither barley and oat flour courses the dough to raise because they do not have any wheat gluten, so both grains are good for crackers and crispbread.
I baked a batch of these the other day and they are really lovely. I baked them on a dry frying pan, but I bet they would be great on a pizza stone as well. I think much historical baking would work better on a pizza stone than on a normal baking tray.
I store mine in a tin so they don’t get too soft.