|Here he is turning a symbol of Roman authority on its head. I wonder if that's a metaphor.|
Rome and Carthage were locked in a nasty feud for control of the Mediterranean. Hannibal, the top general of Carthage, was coming off of a pretty sweet victory at Lake Trasimene, where he had ambushed and routed a Roman army led by one of the two Consuls, the chief executives of Rome. Rome was laying low for a year, opting to avoid large confrontations and instead picking off Hannibal's army little bits at a time. The people of Rome were unhappy with that strategy. They wanted a big, juicy victory they could sing songs about. The government responded by raising an enormous army of around 90,000, under the joint command of the two new Consuls.
Cannae itself was a critical supply depot, and Hannibal kicked off the festivities by snatching it right out of Roman hands. The Consuls were a bit cross about that, so they decided it was time to lay the smack down on this Carthaginian asshole. Everything looked awesome for Rome up until the day of the battle.
Hannibal was a genius with preparation, and was always able to finagle himself into the right environmental position to get an advantage. On this day, he managed to find a spot where the wind and sun were at his back - which meant the sun and dust would go straight into Roman eyes. That was step one.
Step two was his cavalry. Numidians were, at the time, the very best horsemen in the Mediterranean, and they were on Hannibal's side. They were one of his key strengths, and were guaranteed to chase off the Roman cavalry.
Step three was the feet on the ground, and this is where he showed his masterstroke. Roman infantry typically put their strongest units in the center, where they could punch a hole straight through the enemy line. Hannibal responded by putting his weakest units in the center, but stacking it heavily. The result was like a big, umbrella-shaped cushion. When something strong hit the center, the shape would bulge at the sides. And that's exactly what happened.
|Ha! This is gonna be awesome.|
That's when the cavalry came back.
By the time the dust had cleared, up to 75,000 Roman soldiers were dead, and up to 10,000 were prisoners. Hannibal's losses were somewhere around 5,000. It was one of the most crushing and humiliating defeats of all time, and it very nearly caused the collapse of Rome. Luckily for classicists, Hannibal didn't really have the means to capture cities, so he was unable to press his advantage. Eventually, Rome rebuilt and eked out a major victory against Hannibal that led to Carthage's surrender under grossly unfair conditions.
The Battle of Cannae is remembered today largely because holy shit, how did he pull that off? Specifically, because military academies ask that very question (albeit phrased more politely) to all potential officers.
If you're curious about what happened next, the name Hannibal became synonymous with "boogie man" in Roman culture, and Carthage was so intensely reviled that Cato the Elder, a prominent statesman, ended every single speech he gave, no matter what the topic, with the phrase, "Furthermore, I am of the opinion that Carthage should be destroyed."