To Heliodorus, Monk
Heliodorus, originally a soldier, but now a presbyter of the Church, had accompanied Jerome to the East, but, not feeling called to the solitary life of the desert, had returned to Aquileia. Here he resumed his clerical duties, and in course of time was raised to the episcopate as bishop of Altinum.
The letter was written in the first bitterness of separation and reproaches Heliodorus for having gone back from the perfect way of the ascetic life. The description given of this is highly colored and seems to have produced a great impression in the West. Fabiola was so much enchanted by it that she learned the letter by heart. The date is 373 or 374 A.D.
Source: Letters (New Advent)