Battering rams - who needs them?

Admittedly I'm using the SPQR mod but in my Germania campaign the Gauls, in their innumerable and futile attempts to storm at least one of my towns every turn, have taken to parking their battering rams a short distance away and proceeding to dismantle the gates and walls with their bare hands - well light weapons anyway. They seem to have the gates open in no time at all although the tool tip reads 0% damage. The Britons, Dacians et al seem to be unfamiliar with these tactics

Is this peculiar to SPQR , the Gauls or what?