I think by medieval times the gates would be seen more like a magical barrier between two worlds (the world of men and the hellish world of Gog and Magog). The wild peoples within are contained until the end times. They don't really see the gate in military terms, it is more like a seal that, when broken, will unleash havoc upon the world.
Now the "anchiton" substance may have come into play because of this - to validate the gate's supernatural holding power in absence of any army or garrison.
Now the "anchiton" substance may have come into play because of this - to validate the gate's supernatural holding power in absence of any army or garrison.