I apologise, I stand corrected. I assume you refer to the Achaemenid invasions of Greece, or the campaigns of Chandragupta Maurya? Or perhaps the Warring States period in China?
Total projected numbers:
Achaemenid invasion of Greece (Achaemenid side): 300,000
Battle of Red Cliffs (208-209 AD): 270,000 (Wu estimate) 850,000 (Wei claim)
Battle of Sekigahara (1600): 200,000 (campaign) 160,000 (battle)
Sieges of Osaka (1614-1615): 280,000 (winter) 210,000 (summer)
Having said that, the Grande Armée was larger still, at approximately a million men.