Slope of Mount Amanus The mountain range north of Antioch. Why here and not on the Euphrates? It would appear that the reason that this arch was erected was to commemorate Germanicus' service from one end of the empire to the other, and thus the crucial point was that it be erected in the east. The Euphrates may not have been considered a secure enough frontier at this time, though it is left up to Tiberius to decide this point.