 Complete the following phrase:  The increasing number of fortifications that were falling into decay were renovated again under Emperor Valentinian I 364375 and upgraded to the conform to the latest military tactics. Walls were thickened, and defensive ditches renewed. In addition, towers were built along the walls, such as a watchtower discovered near Oberranna in 1960. These fortifications lasted only another hundred years before the fall of the Roman Empire. In 488 the land of present-day Austria was cleared. The Roman fortifications along the lower courses of the Danube were overhauled once again, especially under Anastasios I and Justinian I They finally served during 