In this old Locomotive Engineers Journal, there is a short discussion of ancient vs modern army sizes. The writer gives a list of very large ancient armies. Most of the items on the list have easy enough sources. For example:
- Xerxes led 2,641,610 combatants and as many non-combatants. Invasion of Greece, Herodotus.
- Hamilcar led 2,000 ships and 3,000 smaller vessels, together with 300,000 soldiers. Battle of Himera, Diodorus Siculus. There is a typo here: 2,000 should be 200.
- Timur had 1,600,000 soldiers against Bayezid, who had 1,400,000. Battle of Ankara, Johann Schiltberger.
However, one of the items on the list I couldn't recognize:
"The city of Thebes had 100 gates and could sent out at each gate 10,000 fighting men and 200 chariots - in all, 1,000,000 men and 20,000 chariots."
This is obviously referring to Egyptian Thebes, but searching for this number only reveals a similar list. In the War Scrap Book of Matilda Gage, a similar list of vast armies in ancient times is contained:
- Some items in the journal's list, like the Battle of Ankara, are omitted.
- Other items, like the Battle of Cannae (80,000 infantry, 6,000 cavalry, Polybius), are only present on Gage's list.
- In both lists, the claim about Thebes is repeated, and is the first item on the list.
Since these are mostly famous battles, it is possible the two lists are totally unrelated. They seem to be organized in loose chronological order, so it seems the claim about Thebes should be in very ancient Egyptian times. But I cannot find where it comes from.