ROMAN DISHED SHIELDS

[Medicus matt]

It would be interesting to know whether RATers with an experience in making shields may come up with an alternative explanation of this phenomenon or whether it may really imply that most or even all shields were dished.

You get the same evidence when you look at the bosses from early Anglo-Saxon cemeteries. Having made lots of shields (flat ones, lenticular ones, ones curved in one plane), I've found that the angle of the flange on the boss can't be taken as an indicator for the shape of the board.
Whilst you usually do need some shaping of the flange to ensure a good fit on a lenticular board (altough even this depends on the extent of the dishing at the centre of the board), a shaped flange also ensures a very secure fit on a flat board. Rivetting a shaped boss onto a flat board puts the flange of the boss under compression, meaning that it's much more secure and maybe means that it's able to absorb impact more effectively.

And of course it may be that in many cases making the flange perpendicular to the wall of the boss was deemed to be an unnecessary step in the manufacturing process.

I've not thought to check, but given that a lot of bosses from AS graves are found with their nails in situ, it should be possible to analyse these to see if there's a space between the inside of the boss flange and the wooden board.