Rectangular shields B.C.?

[Carlton Bach]

Bear in mind that not all square shields belong to the scutum tradition. Hellenistic sports festivals sometimes included among their combat sport events a contest of 'thyromacheia' - 'door-fighting', which is the counterpart to hoplomacheis, traditional armoured shieldfighting. It is thought that that 'door' is a large shield, similar to a scutum, but quite possibly its own kind. My first guess would be Balkan Celtic, but it's really not so unintuitive a shape for shields.