In ancient warfare, how was it possible one side loses tens of thousands while the other only dozens (e.g. Battle of Carrhae)?

Because warfare is only fair when you get into a punching contest. Stabbing someone in the back is more effective and has less risk. This is not hyperbole. One of the greatest fears in ancient combat was that one’s army would rout (begin to run away). At which point, enemy soldiers could, literally, just run yours down and stab them in the back.

But there are other ways to attain “stab them in the back” status.

• You could have your men trained to elite status such that they are unlikely to be killed by a common soldier (Spartans at Thermopylae)
• You can rely on flanking maneuvers (German Blitzkrieg)
• You can attack at night or by surprise (Six day war)
• You can have superior air or ranged cover (Gulf War)
• You can have better fortifications (Siege of Malta)

Or, in the case of Carrhae, you can have an incompetent general on the other side.

Marcus Crassus

To be frank, the only reason Crassus was commanding an army on the Roman frontier at all was because he was trying to emulate Caesar’s victories in Gaul and Pompey’s victory over Mithradates.

But while Crassus was an experienced soldier (he fought for Sulla during the Roman civil war), he had no merit as a commander. He was lazy, reckless, and unimaginative.

Let’s go through Crassus’ mistakes.

1. Crassus turns down Artavazdes’ offer of 46,000 additional troopsIncluding 16,000 cavalry. If Crassus had accepted the offer, his cavalry detachment alone would’ve outnumbered the Parthians at Carrhae.He also ignored Artavazdes’ advice to go through the mountains. The king of Armenia probably knows a little bit about fighting the peoples who live on his border.
2. His intelligence-gathering was abysmalAdmittedly, Crassus was tricked by a traitor named Ariamnes. But leading your army into a desert without understanding the local water sources is a rookie mistake.Further, he was surprised to learn that the Parthians even had a force in the region. That’s the sort of thing you’re supposed to pay attention to.
3. He trusted his son over his generalsPublius Crassus was eager to fight and convinced Crassus to launch an immediate attack without letting his men rest.Worse, he put a river at his own back so his men were unable to retreat.
4. He chose the wrong troop formationRather than spreading out into a battle line, Crassus ordered his men to form a defensive square. I’m a bit torn on including this one, because if Surena had gone with his first instinct and ordered a full-on charge I think the Romans would’ve won this battle.But banking on your enemy making a foolish mistake is not good strategy, especially when it hurts you if they do the smart thing. In this case, the formation prevented the Romans from engaging the more mobile enemy.
5. … twiceAfter that, Crassus tried the Testudo (turtle) formation. But that one is weak to cavalry charges.*facepalm*
6. Then he froze.Having run out of other strategies, Crassus eventually just panicked and shut down. He decided to wait till the Parthians ran out of arrows.This is a perfectly legitimate tactic, in conjunction with a larger strategy. Archers do run out of arrows with alarming rapidity. But just sitting there and waiting for it to happen is rarely a good strategy.
7. Then he tried the desperation hail-Mary playCrassus sent all his cavalry to chase down the horse archers. But they over-chased, and he did not call them back, and they were cut off and destroyed.
8. Then he tried to double downCrassus orders a general advance??Not much to say here except that the question marks are chess annotation
9. Then waits too long to retreatIf Crassus had retreated earlier, he could have done so in good order and maybe only loses a quarter of his men. Brutal, certainly, but still leaving him with a force 3x the enemy size.

So it turns out that one of the easy ways to get a bloodless victory is to have your opponent flail about ineffectually the entire battle like a beached whale.

Credit: Kevin Yue