Why did the Byzantine Coinage Turn Concave? Old Suggestions and a New One

The concave shape of some Middle Byzantine coinage is one of its most striking features to the uninitiated, but not all scholars have been equally intrigued by the phenomenon. Many have dealt with the subject in only a few lines. More work has focused on the technical question of how the coins were struck this way than on that of why, and none of the reasons proposed have been wholly free of difficulties. This paper briefly reviews those explanations and their problems and then offers a further possibility which may avoid most of the difficulties.