I am having trouble defending my cities. The AI will usually bring at least a dozen units in a stack with several seige devices and park his army on an adjacent hill or forest square, leisurely reducing the city defenses to zero. I play on prince and find I simply cannot keep up with the enemy unit production levels, so I usually must win by superior strategy. However I have no idea how to defend my cities properly in this scenario. I either end up hoping to make peace berfore the defenses hit 0% or I am forced to attack, but since I cannot attack his seige engines until all the other units on the tile are destroyed, it makes me, the defender, into the disadvantageous attacker. Is there a counter to this other than having simply many more units than the AI? Must we as the defender always be forced to attack the enemy army once it reaches the city?