When was the roman empire largest?

The largest Roman army to ever take the battle field was in 216 BC at the battle of Cannae against Hannibal. The Roman army numbered 85,000 to 110,000 depending on the different sources. Hannibal's army numbered around 35,000 to 45,000. And guess what the Romans lost, hell they didn't just loss they got annihilated. They lost 85% of the army that day. According to some accounts the Roman's dead numbered around 50,000 to 70,000 and another 10,000 to 15,000 captured. The battle on Cannae introduced a new concept in warfare, the Battle of Annihilation. If one takes that the mid range of the number of Roman's dead of 60,000, Cannae was the single bloodiest one day battle in Human history even to this day. Only the dropping of the atomic bombs on Japan surpass it.