WI: Persia becomes Christian before Rome

Prior to the advent of Islam, Persia had a rather large Christian population. Despite the Zoroastrian clergy objection and displacement, what would happen if Persia becomes Christian before Rome does? Would Rome still adoppt Christianity as its official religion?

Not likely.

The Nestorian Population was mostly made up of the Assyrian population of Assuristan. Arabistan of Hira had the Nestorian Lakmids but, they truly converted rather late in the 6th Century.

Yazdegerd was described as a friend of the Christians and for that he received a great deal of flak. After Kartir influenced Hormzid then the Sassanid Church is rather set and will prevent any attempt at conversion.