Q: In January of 49 BC, after Julius Caesar had conquered the Gauls, he and the 13th Legion (Legio XIII Gemina) marched toward Rome. When they got to the Rubicon River in northern Italy, the triumphant general stopped to perform a rite, saying, “Alea iacta est!” Meaning “The die is cast!” What was ‘the die’ anyway? And why did he cast it?
A: Roman generals, when faced with an important decision (like marching on Rome with an army) used divination to see if the gods approved of the actions they planned to take. Divination took many forms. One popular method, called cleromancy, involved tossing or casting lots. You could use dice, knucklebones, or even dried beans in a pinch. Caesar’s dice throw said ‘full speed ahead,’ the good omen that Caesar (and his troops) craved.
(Much more on divination in How to Mellify a Corpse.)