I agree that 1. is probably the "best" alternative. Although I really just see many different bad ones. When deciding whenever to waste time or soliders I do honestly belive that time is the more precious at the moment. Thus lets attack and finish them off before they can entrench themselves even further. Perhaps (although highly unlikly) we may find something of use in the fort. Or else a boost to morale (although a losse of it if we fail).

Hopefully the number of Roman lapdogs inside the fort won't be to high. It's all in Zamolxis' hands...