I was reading about a viking age burial, and apparently it has been theorized that the occupant was a horse archer. This seems mainly to be because "armour piercing arrows" and horses were found in the grave. That seems to be a big jump to me, but got me wondering is there any other evidence of viking using horse archers? I guess the idea is that it would have been adopted from contact with the east, and there is eastern elements in the grave.

I think that pretty much every culture with horses has people who shoot or throw things from horseback. Eg. the Norwegian King's Mirror from the thirteenth century mentions offhand that its good to shoot a crossbow or a hornbow from horseback.

I’ve never come across King’s Mirror and as one interested in very early crossbows that quote is very useful. Thanks for posting

https://www.patreon.com/posts/domed-round-in-28052167 At bottom there's a bit of info on the possibility of viking cavalry.