Actually some Classic Era battles were also exaggerated, especially by the historians of those times, sometimes to the point of ridiculousness.

Anyone read up on the Persian Wars? Herodotus wrote at at Thermopylae there were 5.3 MILLION soldiers!!! Other contemporaries estimated it at 800,000, which still doesn't seem realistic. One Persian source says this is so.

However, modern estimates place the actual number around 120,000.

Considering that the world's population wasn't so great at that time, an army of 5.3 million would be crazy. It would also be a logistical nightmare moving so many troops, which can also be a reason why medieval battles were smaller.

That said, constant warfare would severely deplete kingdoms of able-bodied men. By drafting lots of peasants, it would mean lands would go untilled and a lord would lose out on his tribute. (Correct me if wrong here)

And that said, it would certainly be awesome if 5.3 million men made a massive charge on the battlefield!