The gate that was later called that of St.George was apparently the old Rhodion Gate. This gate would have been named after the quarter of the city where the Rhodian contingent of immigrants were settled by the early Seleucid rulers. This zone either corresponded to the Kerateion quarter (in reality the Jewish quarter) or was even more elevated than the Jewish district.
Boucher in his Short History of Antioch refers to the origins of the Rhodion name as being with a "rose garden" rather than any settler history.
The prime mention of the Rhodion Gate is in Malalas where he relates the construction of the Theodosian Wall:
"Imperator ¡taque jussit, uti aedificia etiam quae extra urbem posita erant muro cingerentur : murus ¡taque factus est, a Philonauta quam vocant Porta Rhodionem usque dictum locum.."
We can merely speculate on why the old Golden Gate ceased to function as the main point of egress to the south. Maybe the bridge over the Phyrminus opposite the main gate was no longer usable. Maybe the higher gate was easier to defend. As the Rey map shows the St George's Gate was certainly rather distant from the village that Antakya had become by the time of his survey.
In any case, this adds another gate to the list of the those in the city walls.