Research Notes:

Following a new agreement between Rome and Persia, Khosrov’s son, Trdat II (217-252), was crowned King of Armenia. By the established tradition, he received his crown from the Roman emperor, in this case, Macrinus. Trdat II, however, was the first Arsacid king who was raised in Armenia and who followed his father as King of Armenia. His long reign, combined with the civil wars in Rome, not only enabled Armenia to take a respite from the East-West rivalry, but to separate itself from the Persian Arsacids and establish a fully Armenian branch—the Arshakunis—at the start of the third century. ¹

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Tiridates II is mentioned as king of Armenia by the Greco-Roman historian Cassius Dio in his account of the reign of the Roman emperor Macrinus (r.217-218). He had come to power after the assassination of Caracalla and had inherited a war against the Parthian Empire. Apparently, Cassius Dio referred to a war against Armenia as well in a lost part of his Roman History. Macrinus tried to stabilize the situation by recognizing Tiridates.

The warfare carried on against the Armenian king, to which I have referred, now came to an end, after Tiridates had accepted the crown sent him by Macrinus and received back his mother ... together with the booty captured in Armenia, and also entertained hopes of obtaining all the territory that his father had possessed in Cappadocia as well as the annual payment that had been made by the Romans.[Cassius Dio, Roman History 79.27; tr. Earnest Cary.]

We can only deduce that Tiridates' father - perhaps the king known to modern historians as "Chosroes" - received payments and was in control of parts of Cappadocia, but the details are not well-understood.

Without naming Tiridates, Cassius Dio refers to him a second time in his account of the rise of the Persian Empire of the Sasanians. Its king Ardašir has defeated his former Parthian overlord Artabanus IV and is now subduing the territories that had once been held by the Parthians.

Ardašir made a campaign against Hatra, in the endeavour to capture it as a base for attacking the Romans. He actually did make a breach in the wall, but when he lost a good many soldiers through an ambuscade, he moved against Media. Of this country, as also of Parthia, he acquired no small portion, partly by force and partly by intimidation, and then marched against Armenia. Here he suffered a reverse at the hands of the natives, some Medes, and the sons of Artabanus, and either fled, as some say, or, as others assert, retired to prepare a larger expedition. [Cassius Dio, Roman History 80.3.2-3.]

A last reference to Tiridates II can be found in the History of Zonaras, a Byzantine author. During the reign of the Roman emperor Trebonianus Gallus, he tells,

Armenia was subdued by them, its king, Tiridates, having fled, and his children going over to the Persians. [Zonaras, History 12.21; tr. Thomas Banchich and Eugene Lane.] ²