I have just received a coin for comparison with the OP coin. It's from an issue that matches that of the obverse of the OP coin but from a known...
I believe that the first strike was quite off-centre. It was to the right of the second (mainly visible) strike. The odd bit of hair in the middle...
Caracalla. M AVR ANTON CAES PONTIF / PRINCIPI IVVENTVTIS
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