As I was contemplating why the Roman Legionary fought, Spiff brought up a well known fact that completely eluded me and that is the majority of the legions were loyal to their General and not to the state or empire. Because of this loyalty, the Empire was crippled by multiple civil wars over the years for the title of Emperor. After the death of Nero, which was the end of the Julio-Claudian Dynasty, several men such as Servius Sulpicius Galba, Marcus Salvius Otho, Aulus Vitellius, and Titus Flavius Sabinus Vespasianus vied for title of Emperor from 68-69 AD. As Galba failed to secure his role as Emperor with his corrupted and perverse form of government, the army revolted against him and swore their allegiance to the Senate and the people of Rome and demanded a new Emperor. It was so bad for Galba that Commander Hordeonius Flaccus of Upper Germany couldn't get his troops to renew their loyalty to Galba. Galba's next mistake was to appoint Lucius Calpurnius Piso Licinianus as his son and heir which greatly angered Marcus Salvius Otho. Otho wanted to be Emperor himself and so he conspired with the Praetorian Guard to get rid of Galba and his newly announced heir. In 69 AD, the Praetorians murdered Galba and Piso in the forum, cut their heads and presented it to Otho.
Marcus Salvius Otho was very popular within the army and he used this popularity and the distaste the army had for Galba to easily convince the Praetorians to murder Galba and secure his role as the new Emperor. Even though the man had very few links to the army, he depended more on the soldier's support then any of his predecessors. Since he wasn't in constant contact with the army, he couldn't hold their favor for him and General Aulus Vitellius soon had wide spread support from the army to overthrow Otho. Emperor Otho did his best to avoid civil war by offering Co-Emperorship to Vitellius but Vitellius didn't want to share power so his Legions began their march into Italy. Otho did still have support from the Danubian legions which gave him the advantage of superior forces but the problem was they had to march from the Danube all the way to Italy. Otho needed all the time he could get but Vitellius' generals Valens and Caecina knew this and so they built a bridge over the Po River crossing into Italy. Instead of giving himself more time for the Danubian legions to come to his aid by retreating deeper into Italy, he chose to make a stand and fight it out with the legions he had at his disposal. Otho's legions were defeated in the Battle of Cremona, 69 AD. Othos wasn't at the battle, he was in Brixellum and after hearing of his defeat, he chose to commit suicide in order to end this civil war.
Aulus Vitellius, who wasn't even a military man and had no knowledge of military warfare, was given the command of the Lower Germany legions by Galba. Because of the hatred the legions of Upper and Lower Germany had for Emperor Galba for refusing them a reward for their part in the suppression of Julius Vindex, Vitellius easily gained his legions support and had them set out for Italy in the command of General Valens and Caecina to overthrow Emperor Otho. After his legions defeated Otho at Cremona and hearing of Otho's suicide, the newly appointed Emperor marched into Rome in a glorious triumph. Emperor Vitellius then proceeded to gain the loyalty of the other legions across the Empire through couriers. Vitellius knew that he was Emperor only because of the German legions and so he rewarded them by disbanding the Praetorian Guard and Urban Cohorts and giving his men their jobs. He also realized that if he was to anger or disappoint his legions, they could remove him just like they did to Otho. Here's where the loyalty of legions plays an important role again. After three months as Emperor, word was getting around that the Eastern legions were beginning to revolt. A battle hardened General by the name of Titus Flavius Sabinus Vespasianus, was gaining wide spread support from the Eastern legions. By July 1st, Vespasianus finally had enough support to march on Italy and overthrow Vitellius. One of Vitellius Generals, Caecina, tried to change his allegiance from Vitellius to Vespasianus but didn't have the loyalty of his troops and was quickly arrested. General Primus of the 6th legion in Pannonia and Cornelius Fuscus, imperial procurator in Illyricum, declared their allegiance to Vespasianus and invaded Italy with around five legions, 30,000 men. The decisive battle was fought yet again in Cremona in Oct. 24, 69 AD with Vitellius as the loser. A couple of months later, the legions of Primus and Fuscus marched on Rome, fighting their way into the city and found the brave Emperor Vitellius hiding in a door-keepers lodge in the palace with a bunch of furniture sealing the door. The Danubian legions broke the door down and found Vitellius disguised in filthy clothes with a money belt around his waist. Vitellius was then dragged out onto the streets of Rome, half naked, all the way to the forum where he was tortured and killed. His body was then thrown into the Tiber River ending the short reign of Emperor Vitellius and the first crisis in Rome. With Vespasian as Emperor, he had the supreme loyalty of the army and would never fear another revolt as long as he lived.
This all proves that one of Rome's greatest weaknesses was its army’s loyalties to their Generals. Once an Emperor was firmly established with general consent he did not need to fear revolt unless he made himself hated by the army or more importantly, the Praetorian Guard. No matter how long Rome remained an empire, the succession of its Emperors would always be determined by the support of the legions and the Praetorian Guard. When it all comes down to it, Rome foolishly weakened itself by constant civil wars by it's legions who wanted their General to become Emperor. If the legions remained loyal to the Senate and the people of Rome instead of declaring their loyalty to their Generals, would Rome have remained a Republic until its end? Would it have still evolved into an Empire controlled by one man instead of a body of elected senators? In many ways the tale of Rome truly goes hand and hand with Durant’s saying, "A great civilization is not conquered from without until it has destroyed itself from within."