Ancient army numbers

[Macedon]

One last thing.. We cannot make comparisons between Napoleon's expedition and this of Xerxes for many reasons. Xerxes was fortunate enough that :

1. There was a direct sea route that he could use to bring supplies from his supply centers

2. The distances are vastly different. You cannot compare a march from Sardis to Athens to one from Paris (or even Warsaw) to Moscow... you just cannot.

3. The Persian Empire had many more resources, much more manpower and certainly much more control over its vassals and armies (yes I understand that this is debatable, it is my personal opinion and even without it, the other arguments are still more important).

4. The timetable of the expedition was very shorter.

5. Moscow was landbound. If his goal was Petersburg things would be much easier.

So, would it really be such a huge problem for Napoleon's France to invade Belgium with 1 million men, or Holland through an allied Belgium, especially if Great Britain did not control the sea?

See how Xerxes never deviated from his course? He did not even try to go to Epirus or Acarnania. Just Thermopylae and then Athens... A mere 200 km in "enemy territory". And then one sea battle and he was back.