After a series of reforms, the army became highly trained, and was well equipped in the middle of the Roman Imperial period. The Romans also had a powerful navy that ruled the Mediterranean and the European Atlantic coast. In the late Imperial period the military's numbers were significantly increased to cover the borders and keep internal peace. The circumstances of the Empire had changed; the Western Roman Empire now relied heavily on units of mostly Germanic tribes living within the borders, who fought in the name of Rome during the Migration Period.