Turkey is a land of many interesting archaeological sites, and I would very much like to go there some day! One of them is a curiosity — a site in the minor Hellenistic kingdom of Commagene, at a place today known as Nemrud Dag in South-Eastern Turkey, adjoining Syria. There is a website for an International Nemrud Foundation, which, if you can get past the awful intro, gives a lot of useful information.
The kingdom was a mixture of Hellenistic and Persian in influence. The kings took names like Mithradates and Antiochus and were related to both the Seleucids and the old Persian Achaemenid dynasty.
The site at Nemrud Dag consists of a large tumulus, with three terraces below it on which are a number of statues and inscriptions. The inscriptions are online, in image form, with translations, here. Apparently they all appear on the west terrace.
Therefore, as you see, I have set up these divine images of Zeus-Oromasdes and of Apollo-Mithras-Helios-Hermes and of Artagnes-Herakles-Ares, and also of my all-nourishing homeland Kommagene; and from one and the same quarry, throned likewise among the deities who hear our prayers, I have consecrated the features of my own form, and have caused the ancient honour of great deities to become the coeval of a new Tyche. Since I thereby, in an upright way, imitated the example of the divine Providence, which as a benevolent helper has so often been seen standing by my side in the struggles of my reign.
Adequate property in land and an inalienable income therefrom have I set aside for the ample provision of sacrifices; an unceasing cult and chosen priests arrayed in such vestments as are proper to the race of the Persians have I inaugurated, and I have dedicated the whole array and cult in a manner worthy of my fortune and the majesty of the gods.
The deities are syncretistic. In each case a Persian deity is associated with Greek deities. Thus we have one statue identifying Zeus with Ormazd (reasonably enough), and another associating the minor Zoroastrian figure Artagnes with the hero Heracles and the god Ares.
But the other item is interesting in a wider sense: a deity “Apollo-Mithras-Helios-Hermes”. By analogy with the other gods, one of these gods must be an oriental, a Zoroastrian Persian deity. Obviously Mithras is the one, as the others are all mainstream classical Greek gods.
But this is a site built by a semi-Persian king, for the purposes of syncretism. This must mean, therefore, that “Mithras” here means the oriental deity Mitra, known to Zoroastrianism.
Some have tried to use this site as evidence that Roman Mithras was around during the first century BC. But there is nothing here suggestive of Mithras of the legions. There is no Mithraeum, no bull sacrifice, nothing. There is an association with Helios, the sun, just as Mithras is associated with Sol. But such an association by itself is not a fingerprint for Sol Mithras, as many deities were associated with the sun, and Mitra himself replaced the Zoroastrian sun god.
I think we must consider Nemrud Dag as a syncretistic site with no connection to Mithras.
There is discussion of the site at the Encyclopedia Iranica site here.