#yohanan

The name John is a theophoric name originating from the Hebrew name יוֹחָנָן‎ (Yôḥānān), or in its longer form יְהוֹחָנָן‎ (Yəhôḥānān), meaning "Yahweh has been gracious". Several obscure figures in the Old Testament bore this name, and it grew in popularity once borne by the high priest Johanan

Why didn't ancient Romans give foreign names to their children?

The Romans began giving Greek names to their children during the pagan era. There was even an Arab dynasty of Roman emperors from Emessa in what is now Syria. So you have names like the emperors Philip the Arab, Elagabalus and Diocletian. Then did when Christianity was legalized by Constantine in 311 AD. Many Hebrew, and Aramaic names from the New Testament were given to children. Yaakov became Iacobus. Centuries later Iacobus became James. Shimon became Simon. Yohanan became Iohannes, ie John. Bar Tolmay became Bartholomaeus, Bart. Bar Nabi “son of the prophet" became Barnabas or Barney.