Parthian princes were allowed to be hostages in foreign lands for the very reason that then it was always possible, if their own monarch displeased them, for the people to obtain a king from abroad, brought up under milder influences.
This harangue was made before the Emperor Claudius and the assembled Senate, Meherdates himself being also present.

Claudius responded to it favorably.

He would follow the example of the Divine Augustus, and allow the Parthians to take from Rome the monarch whom they requested.
That prince, bred up in the city, had always been remarkable for his moderation.

He would (it was to be hoped) regard himself in his new position, not as a master of slaves, but as a ruler of citizens.

He would find that clemency and justice were the more appreciated by a barbarous nation, the less they had had experience of them Meherdates might accompany the Parthian envoys; and a Roman of rank, Caius Cassius, the prefect of Syria, should be instructed to receive them on their arrival in Asia, and to see them safely across the Euphrates.
The young prince accordingly set out, and reached the city of Zeugma in safety.