"Where did you say your artefacts came from? "

The illustration is not very clear here, but the general idea is: "A Map of the Distribution of Roman Coins Found in Eurasia and North Africa" (actually "Distribution of coins in CHRE database by Findspot" [Hekster, Olivier and Manders, Erika 2022, 'Coinage in the Roman Provinces: the RPC and CHRE projects',* Journal of Roman Studies. 112. 1-15. 10.1017/S0075435822000326]).

* RPC -Roman Provincial Coinage ; CHRE - Coin Hoards of the Roman Empire project.