@Andrew McCabe . A fellow collector got one from the same auction as I, and your Caesar came from this auction as well if I'm not mistaken. His had a mention it was purchased at Robert Ball in Berlin.
Thanks! The Robert Ball reference helps once again to nail the date to early 20th century. I might look at Ball catalogues just in case. Consistent story emerging.
I found additional provenance for mine in a 1960 FPL, sadly no other provenance for the coin in question: