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View of a relief showing Artemis, on the left with two dogs (or stags?), and Serapis on the right. The relief is said to date to AD 238–244.
Serapis was a Greco– Egyptian– deity associated with abundance and resurrection. In some contexts, he seems to have replaced Osiris as the consort of Isis.
If Isis and Artemis have blended together here at Ephesus, and there is some evidence of this, possibly this explains the appearance of Serapis with Artemis/Isis on this relief
Gary Hoag, cites R. E. Witt approvingly, noting "how Artemis and Isis have interchangeable roles and identities in the thinking of Xenophon of Ephesus" (Hoag, p.83 and see 83–93). A document which Hoag and others now date to ca. AD 50!
Hoag, Gary G. Wealth in Ancient Ephesus and the First Letter to Timothy: Fresh Insights From Ephesiaca By Xenophon of Ephesus. Winona Lake, IN: Eisenbrauns, 2015.