Well Tim that is true. The historians of that era wrote for about 1.000.000 troops, but that is exagerating. It believed by modern historians that Darious fielded 400-500 thousand men. Macedonians 55.000. And they would propably had lost the battle if only Alexander did not routed Darious himself. The battlefield was so vast that when the right flank Persian cavalry smashed the Greek left they thought that they won the battle, and they could not see the rest of their army routing.