The dramatic change in the abilities of Greeks to operate against fortifications owed much to the development of effective artillery.
This had begun around 400 BC in Syracuse under Dionysius I. By Alexander’s time, torsion-powered artillery was in use.
Torsion machines used skeins of sinew or hair rope, which were wound around a frame and twisted so as to power two bow arms; these could develop much greater force than earlier forms (such as the gastraphetes) reliant on the elastic properties of a bow-stave.
Two forms of such ballista were used by the Macedonians: a smaller bolt-shooting type called the oxybeles and a larger stone-throwing machine called the lithobolos.
The largest lithoboloi could fire stones up to 80 kg in weight.
Such machines could shower the defenders of a city with missiles and create a breach in the walls themselves.

 Alexander the Great appears to have been one of the first generals to employ artillery on the open field of battle, rather than in a siege.
He used massed artillery to fire across a river at a Scythian army, causing it to vacate the opposite river bank, thus allowing the Macedonian troops to cross and form a bridgehead.
The dramatic change in the abilities of Greeks to operate against fortifications owed much to the development of effective artillery. This had begun around 400 BC in Syracuse under Dionysius I. By Alexander’s time, torsion-powered artillery was in use. Torsion machines used skeins of sinew or hair rope, which were wound around a frame and twisted so as to power two bow arms; these could develop much greater force than earlier forms (such as the gastraphetes) reliant on the elastic properties of a bow-stave. Two forms of such ballista were used by the Macedonians: a smaller bolt-shooting type called the oxybeles and a larger stone-throwing machine called the lithobolos. The largest lithoboloi could fire stones up to 80 kg in weight. Such machines could shower the defenders of a city with missiles and create a breach in the walls themselves.
 Alexander the Great appears to have been one of the first generals to employ artillery on the open field of battle, rather than in a siege. He used massed artillery to fire across a river at a Scythian army, causing it to vacate the opposite river bank, thus allowing the Macedonian troops to cross and form a bridgehead.
Ancient Macedonian army