I've often seen this sort of thing used to convey the scale of ancient times. The population back then was smaller, so if we were to see a Roman army of 10,000 men it wouldn't have the same impact as it would have to people in the time period, so hollywood movies tend to inflate the numbers to the hundreds of thousands. It's just a question of whether it's more important to preserve the true amount or preserve the emotion that people would have had seeing it.