Having recovered from their losses at Trebia (218 BC) and Lake Trasimene (217 BC), the Romans decided to engage Hannibal at Cannae, with roughly 86,000 Roman and allied troops. The Romans massed their heavy infantry in a deeper formation than usual, while Hannibal utilized the double-envelopment tactic. This was so successful that the Roman army was effectively destroyed as a fighting force. Following the defeat, Capua and several other Italian city-states defected from Rome to Carthage.