The present letter is not dated, and it can be said only that it was written at some point during the episcopacy of Ambrose. Palanque's (1933) attempts to fix the date for Letter 18 (and the letters following this one and concerning similar topics) are too fragile to be followed (see Mazières 1973). Here, Ambrose's addressee is here Orontianus, who is treated with paternal affection. In the last part of the present letter, Ambrose mentions that Orontianus was baptized at an early age ("from the first flower of your youth an heir of the Church"), had a sacred ministry in the Church (possibly the diaconate), and was then ordained by Ambrose to presbyterate ("persevere in your purpose, remembering God's grace and His gift which you received by the imposition of my hands. Thus, in this office, too, as in the sacred ministry, you may reveal your faith and diligence and look for the recompense of the Lord Jesus"). Palanque conjectured that Orontianus was of Eastern, possibly Syrian origin, but his arguments - an alleged knowledge of Greek by Orontianus, and the fact that he must have been away from Milan to receive letters from Ambrose, are unconvincing. Mazières (1973: 52-54) also discussed an old thesis of the Maurists that Orontianus might have been of Jewish origin. Although he rejected the passage originally used to claim this (Letter 20.15), he traced other passages and recurring topics (concerning the role of the Jewish people in the history of salvation. Here, in Letter 18 it is a conversion of a weak soul, "like Israel according to the flesh", par. 19) referring to the personal experience of Orontianus that made this conjecture possible.