Quote Originally Posted by Kralizec
A bit late, but I feel compelled to respond to this. I don't mean to crack you down, but this is a blatant inaccurate portrayal of facts.

Carrhae took days, not hours. As you said the horse archers (wich weren't drawn from Persians, correct me if I'm wrong) were so effective because they had an unlimited supply train of arrows. If you play EB or especially vanilla RTW with limited ammo off, it's easy to score a victory with negligable losses. That is, unless the Roman player is smart and brings in a good number of slingers and auxiliary archers, wich is exactly what the Romans did afterwards and enabled them to put up more of a fight against the Parthians in later battles.
A lorica hamata coupled with a scutum offers excellent protection against arrows, and when in a testudo formation legionaires would be nigh invulnerable to archers. The Parthian general realised this and charged with his cataphracts or just feigned charges, so to force the Romans to break up their testudo because it's a specialised formation that's no good in close combat, let alone warding off cavalry charges. The continuing cycle of charges of heavy cavalry, followed by massive barrages of arrows, proved exhausting to the Roman infantry and destroyed their morale.
I'm not entirely sure what happened after that, I think Crassus accepted a Parthian invitation to negotiate, but it was a trap...the Romans later tried to escape but were rolled over by the Parthian cavalry.

Crassus was a fool trying to fight an enemy that prefers horse archers with an army consisting almost entirely out of heavy infantry. The Armenian king actually tried to warn him I believe, but he ignored his advice. Horse archers are not an invincible force, but you have to bring along the right tools to fight them.
I have no idea why I said Persian archers...

As to Carrhae taking days, that depends on how you look it. It didn't take more than a day for the Romans to give up and begin a retreat, but they were harrassed during their retreat.