In the years after 500bc new siege weapons were developed. Dionysius, the ruler of Syracuse in Sicily, went so far as to establish an official armaments factory that had a section dedicated to developing new siege weapons. One of the inventions this establishment produced was the siege tower. This was, effectively, a mobile mound. It consisted of a wooden tower mounted on wheels. Ladders inside the tower gave easy access from the ground to the top. At the top was a drawbridge that could be let down on to the enemy walls. All the attackers then needed to do was swarm up the ladders and dash over the drawbridge to enter the fortress. It had the advantage that it could be pushed into position before the defenders could heighten their walls, as they could do against a mound.
Dionysius’ workshop also produced the gastraphetes, or winched bow. This consisted of an enormously powerful wooden bow mounted on a stand. The bow was too powerful for any human to draw. Instead it was equipped with a ratchet system operated by a winch so that the bow could be pulled back gradually by teams of workers. It fired an arrow much heavier than that used by conventional hand bows over a far greater distance, perhaps as much as 300 metres.
from THE BATTLE OF THE GRANICUS by Rupert Matthews