Uggeri speculates that this gate led to a rugged route up the valley of the Parmenios river and over the ridge (before the building of the Iron Gate dam made the route impassable). This led to Apamea by a more direct, but much more topographically challenged, route than that which went out the Beroea Gate and followed the Orontes to Apamea the long way.
The Mese Pyle has not been found and there are very few mentions of it in historical texts. One of these references though is from Malalas who records that it was adorned with a statue grouping of the Wolf & Twins (which also decorated the Beroea Gate according to the same source). Morey states that the Middle Gate was near the Temple of Ares, but does not say what source attested to that comment.