Rome\'s Public Enemy #1

[Theodosius the Great]

Enemies are often only enemies in the mind. ...

Quite true. Most of the enemies listed by the posters were not aggressors against Rome.

Warning, here's my unsolicited anti-thesis

Rome was the aggressor in all three Punic Wars, the Macedonian Wars, the Mithradaic Wars, the Greek Wars (southern Italy), the Iberian Wars, the Parthian Wars, and some of the Persian Wars. The greatest enemy is always the one bent on conquering / destroying you. The Teutons and Cimbri remain the best candidates for "Number 1", IMO. They were invaders and they could not be reasoned with or bought off unlike the Gauls (who were bought off after the sacking of Rome) or Attila (who was also likely bought off by the Pope). Spartacus was simply a freebooter who wanted to raid as much as possible before escaping from Italy. Hannibal and Pyrrhus were very willing to sign treaties but Rome's stubborness prolonged the wars. The Parthians were not expansionists. The Persians had limited territorial designs on the Eastern Meditarranean. The Hellenistic Kingdoms couldn't have cared less about Western Europe. So, none of them could qualify as the greatest threat to Rome.

Perhaps a close "Number 2" enemy would be the Vandals. They were bent on destruction and conquest. They created nothing and left destruction in their wake when they could not conquer. Or the Arabs could be "Number 2". They laid siege to Constantinople many times and almost took it. They ended up conquering two-thirds of the Eastern Empire and went on to conquer former Western imperial provinces. The Arabs were relentless and bent on conquest in all directions. Occassionally you could buy them off but that was not a permanent solution. Sooner or later they would come back. Only their own civil wars did them in. Next came the Turks but they had designs on the other Muslim caliphates rather than Constantinople before the Battle of Manzikert. Even after the battle the Empire could have been saved if not for the civil war mentality the Byzantines inherited from the Romans. If we discount the Romans as an enemy, I'm sticking with my original answer - the Cimbri and the Teutons.

~Theo