I have to agree that that is a fantastic book, well worth reading.
The thing with the First Punic War was that is was primarily a naval war, and naval battles tended to have more extreme casualty counts than land battles. I can't think of any land battles from that war off the top of my head that featured more than forty thousand combatants (from what I recall battles tended to feature 10-15,000 soldiers on each side), but the sea battles were huge. The Aegates Islands had both sides contribute over 200 ships; each trireme had about 200 men on it, which means that both navies had over 40,000 sailors, plus marines! And Cape Ecnomus had over 300 ships for both sides, meaning that there were over 120,000 people in the battle! And every ship that was sunk meant that all 200 of its crew drowned... that adds up really quickly. Trireme battles were a really nasty business.
EDIT: Derp, I don't know how I forgot that many of the ships by this time were quinqueremes

... I'm not sure how many sailors a quinquereme could hold, but I'm sure it's a little more than what a trireme could, meaning the numbers I listed were actually even larger!