Why did the Romans found the cities of Mogontiacum and Augusta Treverorum?

The cities of Mogontiacum (Mainz) and Augusta Treverorum (Trier) were founded during the Roman period as the region was incorporated into the Roman Empire in the 1st century BCE.1

The Romans established these settlements as part of their administrative organization of the Gallic provinces, where the region served as a northeastern border territory for approximately 500 years. Augusta Treverorum, originally the civitas-capital of the Treveri tribe, eventually gained significant strategic importance as the capital of the province of Belgica. By the late 3rd and 4th centuries CE, it became a vital seat of government and imperial residence—often referred to as the "Rome of the West"—to ensure the protection of the Rhine frontier and maintain the loyalty of the Rhine garrison and the local population. Mogontiacum similarly functioned as a key military and administrative center along the Rhine, which served as a critical frontier for the empire.123