Most historical sources from that time are highly Apocryphal.

1. The modern numeric system we use today did not exist
2. The people who eventually created "historic" version of these " documents" were born hundreds of years after they supposedly existed, and never actually lived in the places where these events occurred. And even those sources "reporting" on contemporary events are often highly exaggerated. It's very unlikely the Roman Republic could field 100,000 soldiers in a single battle, let alone do it again multiple times in a century. Those same "historians" we source on figures of this era can't even be relied upon to provide accurate numbers on things that happened when they were alive. And in fact they likely inflated or just made them up.
3. Those people likely relied on multiple levels of translations from languages that no longer existed or they did not understand. Provided to them by people who also did not understand those languages.
4. It was very beneficial to spread stories of great historical civilizations at the time as fact. It was not easy to disprove any claims and you could make a lot of money writing and orating stories about great historical empires and events.

Given historical comparisons, the logistics and technologies of the time, I think having 10,000 people living together in a "city" would be quite a feat. Add in communication (almost everybody is what you would consider illiterate), logistics, difficulty of travel, would mean that 10% of a population being able to muster for war would be...optimistic.

It's likely "great battles" of the time took place between hundreds of soldiers on each side. Thousands could have been possible but very rare.