How many years did Rome spend at war with nomadic tribes?

They served 20 to 40 years

Explanation:

Soldiers served as militants in their entire live. A good part of their lives was spent on carrying out military duties such as maintenance of the types of equipment, patrolling, and training. They also carried out the functions or providing the governor with police force during his missions.

They also contributed to the construction of provinces and other civil infrastructures. Besides carrying out the official duties, they enjoyed their commitments which were compatible with the roman religion practices by being subversive politically.