Hmmmm.... I assume that you are talking about towers in Deathmatch.
Ballista Towers usially are essential to:
a) Defend against Elephants (War elephants now can really screw them, but hey, they're still an option)
b) Defend the perimeter where you want to mine gold, have TC's up and spit Villagers to go for resources
c) Defend unit production zones, so that your buildings last longer
The secret is to use ALWAYS strong units (like centurions or elephants) to team with the towers. In RoR, it helps a lot to have lots of Scythes mountinh guard, because Scythes do splash damage, are the natural counters of Siege weapons (Stone Throwers and Catapults) and it is essential to neutralize catapults (the only thing Towers fear).
If you are facing War Elephants (in RoR only) then you must use either ballistas (the best) in stand ground stance, or, the next best, Horce Archers in numbers, in the middle of the towers. Now a note about tower placement.
Towers are best placed as follows:
On top of hills - super best.
Covering each other (essential)
Behind houses or walls (but never close-up, always with 1 tile in between, to avoid spiull damage from scythes, catapults and war elephants).
The more obstacles between a tower and the enemy, the better it is - dealing damage for free!
The most annoying tricks:
If you are being attacked by war Elephants, a few priests hidden back near the towers can really help you to get a bigger, better army, LOL! The most annoying things about Towers:
If you are being hit by Cats and you don't have a good enough reaction force, you'll lose the Towers.
Towers DO NOT go out and kill your enemies. Only your Army can do that.
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Walls and Towers are very good to "entertain" your enemy if you get to wall him up in his town. You super-huge army, that you amassed while you were freely roaming the map for resources, will finish him.
Conversely, if you wall yourself up and are not aggressive, you'll end up losing.
........................................................
Wise_Max is the slowest player on Earth.
But Wise_Max has a lot of fun playing. So, he always wins
even when he loses the game. And he made Friends.
Is that Wise or what?...