I am fighting in Bactria and have besieged one of their towns with 5 Persian archer-spearmen - there were only 2 of their units in the town and I had cut off the town with my main armies. Lo and behold and a relief army emerges out of India and is only a turn away from relieving the town. I have no way of getting reinforcements to the besiegers before they are attacked.

Inside the town there is a stack of medium spearmen and also a Bactrian FM. Is there anyway that I could win this fight? I have enough battering rams to knock open the gates but I just can't see how I could defeat the defenders. I am playing on the usual M/VH setting. Any thoughts?