On the fringes of the Empire, in new conquests or, increasingly, in defense against barbarian invasions, the Roman fleets were still engaged in open warfare. The decline of the Empire in the 3rd century took a heavy toll on the navy, which was reduced to a shadow of its former self, both in size and in combat ability. As successive waves of the "Völkerwanderung" crashed on the land frontiers of the battered Empire, the navy could only play a secondary role. In the early 5th century, the Roman frontiers were breached, and barbarian kingdoms appeared on the shores of the western Mediterranean. One of them, the Vandal Kingdom, raised a navy of its own and raided the shores of the Mediterranean, even sacking Rome, while the diminished Roman fleets were incapable of offering any resistance. The Western Roman Empire collapsed in the late 5th century. The navy of the surviving eastern Roman Empire is known as the Byzantine navy.