Norman, this might interest you.
It was found during building excavations in Colchester and is a fine example of a Roman archer's thumb-ring. The extended piece is designed to sit on the inside of the thumb and reduces chaffing from the bowstring when it is pulled taut.
An example of its usage here:
If you go on e-Bay there are several of these for sale, though whether they're genuine or not is anyone's guess. However their spread over the whole of Roman occupied Europe is a fair indication of how widespread archery divisions were deployed and, one assumes, used.
Incidentally I have read also that it wasn't until the 6th century that Romans (by then largely the Eastern Roman Empire) worked out that one could get more accurate an aim by pulling the bowstring and arrow back to a point before one's face. For pragmatic and ingenious engineers as the Romans were, this seems an amazingly long time to figure out something so basic.