The fickleness of the Roman Legions was one of the "main causes" of the Empire's decline, especially during the disastrous 3rd century A.D. It not only undermined Rome's military power, but Rome's political and bureacratic machine, as well.. . Civil wars was an inescapable problem that plagued Rome from the beginning i.e. the supposed mythical dispute between the brothers, Romulus and Remus. This "problem" was not only due to ambiguity of succession in the principate, but the age old Roman tradition of patronage. . . According to Phillip Spann, “Marius and Sulla learnt the Arcanum rei publicae, the secret of the Republic . . . that power and honors lay not in law and traditions of the Republic . . . but in a loyal army made up of men whose experience in war and devotion to their commander had been forged in extended provincial command, of men who were eager for farms and retirement, men ready to conquer Rome and kill Romans for their general and their price.” This secret was later used by others such as Julius Caesar, Augustus, and Vespasian.. . The military playing field also became more level as Germanic mercenaries adapted legionary fighting techniques and became as efficient and deadly as their Roman counterparts.. . In the end, the early principate was an effective form of administration. It survived the likes of Caligula, Nero, and Domitian. However, by the 3rd century AD., with imperial incompetency becoming the norm and not the exception, Roman generals saw oppurtunities for usurpation, encouraged by their troops no doubt. For example, there were approximately fourteen "barracks" emperors between 235-284 AD. The Germanic invasions and a resurgence of the Parthian empire did not help the situation. It seemed the 1st century BC. was being replayed all over again. This time though, there was to be no Augustus.