Ancient army numbers

[Gaius Julius Caesar]

I wonder.
The Persian empire was vast, had excellent roads, an efficient communication system, well organised goverment of it's provinces. It could draw on manpower from the heart of civilisation, and was able to cross the Hellespont on a pontoon bridge.
But it couldn't organise, mobilise, equip and supply a vast Army?

By any standard before the intersection of booming population, fossil fueled industry, and conscription in the late 19th century, tens of thousands of warriors in one place was a vast army. Six hundred triremes, or 120,000 men, certainly is a vast force! All we can really say about the Persian invasion force was that it had tens of thousands of soldiers (the majority Median, Persian, Bactrian, and Saca infantry with some Greeks and Indians and cavalry), hundreds of triremes, and scared the chitons off the Yauna-beyond-the-sea.

I think there were also Ethiopians, and others from the Middle east as well. All I am saying is when you have a huge army, be it 120,000, or 300,000...you also need the vast logistics train.
He had years to organize this, and the absolute power to get it done.

I wonder if the comparison of the Romans 800 years later, after the region had been plundered and taxed to death by them, in Antioch would really be a reasonable comparison?