Explanation: During the Battle of Carrhae, a series of mishaps and poor decisions by the Roman commander, Crassus, resulted in the Roman heavy infantry under his command coming under constant attack by Parthian lancers and horse archers. Crassus decided, not completely foolishly, that the Roman infantry could simply outwait the Parthian supply of arrows.
Unfortunately for Crassus, the Parthian commander had planned well in advance for the battle, and had a steady camel train of arrows supplying his archers. The Parthians, uh, did not run out of arrows as Crassus hoped, and the Romans were utterly defeated.