We can't do that, otherwise you would build 1 horse unit and a few catapults and take cities without being hit AT ALL. My suggestion would be to increase the base strength of siege units to their current city attack strength (and remove their bonus attack), also give them a 75% defensive penalty when attacked by melee units and a 50% defensive penalty when attacked by ranged units. How often was a catapult destroyed by a stray arrow? can a archer even destroy a catapult, or just the guy launching the rocks. This would allow your siege unit to in most cases not be one shot by a city, likely it would survive 2 or 3 rounds, it would also have the side effect of encouraging melee units on defense. oh, Also I agree with reducing the ranged units attack vs city's by 33% like horse units.