The helepolis, or "Taker of Cities," was one of the most frighteningly clever siege engines ever devised. It was created in 304 bce by the Athenian Demetrius Poliorcetes to assist in taking the city of Salamis on Cyprus. Demetrius was quite interested in taking cities, and was known as "The Besieger" (I am not making this up).
The helepolis was essentially the mack daddy of all siege towers. It stood ninety cubits (that's 140 feet, or somewhere in the neighborhood of 42 meters) tall and 45 cubits wide. The exterior was covered with iron plates and all structural joints were reinforced with iron as well. Sounds heavy, doesn't it?
It was heavy. This bad boy tipped the scales at around 150 tons. It was propelled by approximately 200 men who pushed a wheel that used gears to translate mechanical force to eight fifteen foot tall wheels. It was flipping huge. The armaments of the helepolis were manned by another 200 soldiers.
Ah, the armaments. The helepolis was divided into nine stories. The ground floor was loaded with two 180 pound catapults and one 60 pound catapult. These were set to a low trajectory and were meant to load up debris around the city walls and generally smack down infantry. The next floor was loaded with three more 60 pound catapults. The next five floors made life even more interesting for defending soldiers: each one held two more catapults set for a wall-smashing trajectory and platforms for archers to rain pointy death down on any would-be defender. The top two floor each held two heavy Oxybeles.
Let's see, that adds up to:
Sixteen (16) catapults
Four (4) Oxybeles
Four hundred (400) men in funny skirts and armor
and
One hundred fifty (150) tons of angry metal
bearing down on you.
Cool, isn't it?
Don't put your odds on the helepolis though. It was demolished and the pieces were melted down to make the Colossus of Rhodes.
You can find more information on it at:
http://www.ukans.edu/history/index/europe/ancient_rome/E/Roman/Texts/secondary/SMIGRA*/Helepolis.html
and you can find an awesome picture at:
http://www.geocities.com/TimesSquare/Castle/9645/Ogre/Helepolis.html