Augustus was the first Roman emperor in 27 B.

Roman Empire began under his control. He restored peace and order after 100 years of civil war. The Roman Republic faced many problems during his time. Two of the problems they faced were instability and disunity because of civil wars. Rome had changes that divided the state after its expansion after the Punic Wars and the power of its military increased because of civil wars. Augustus saw what the civil war had done to Rome and he understood that control of the legions by the civil government was needed for peace and order to be established for the Roman Empire.

He wanted to reorganize and make changes in the military to make sure that it wouldn't rise and challenge the law of the state again. Now that the warfare with the Empire was over the role of the legions changed. Augustus also wanted to decrease the number of legions from 60 to 28 to settle the dispute of more than 100,000 veterans in colonies in Italy, Africa, Asia, and Syria. He made a resettlement program with the money of Egypt, which he got after he had defeated Antony. He raised the salary of the troops and made the payment of pensions regular again. He also decreased the threat of soldiers siding with rich generals rather than to the state. He standardized the length of the military service as well.

The Roman legion became a professional and long service and an officer of senatorial rank in which Augustus appointed himself headed each legion. The legionnaires pledged their allegiance to Augustus as commander-in-chief. Augustus recruited soldiers from the Roman provinces in which these troops were granted Roman citizenship if they completed military service. He also raised a new military called the Praetorian Guard to be the bodyguards of the Emperor and to protect the city of Rome from all enemies whether they were foreign or domestic.