Battle of Cannae
After recovering from their losses at Trebia (218 BC) and Lake Trasimene (217 BC), the Romans decided to fight Hannibal at Cannae. The Roman army had about 70,000 soldiers. The Romans massed their heavy infantry in a deeper formation than as usual. Hannibal attacked by using a double-envelopment tactic. That was so successful that the Roman army was destroyed as a fighting force by a Carthaginian army half its size.