C.E. His defeats in Germany convinced him that the empire should not be extended beyond its present frontiers and that Rome's power was limited. Two of his successors broke his policy of defensive imperialism by extending the Roman rule even further. Claudius conquered much of Britain and Trajan took control of Dacia, Mesopotamia, and the Sinai Peninsula. Soon the following Emperors realized that the kingdom had become overextended and they pursued a policy of retrenchment. The Roman Emperor Hadrian withdrew Roman forces from much of Mesopotamia, but he retained Dacia and Arabia. He went on the defensive reinforcing the fortifications along the Rhine and Danube Rivers and also built a defensive wall eighty miles long across Northern Britain. The expansion of the Roman Empire across Europe caused migration, as soldiers and officials moved to conquered provinces to provide defenses and administrative services. By the end of the second century the weakening of the Roman Empire had become apparent. .
The next four Roman Emperors that ruled were from the Julio-Claudian dynasty. They were Tiberius, Caligula, Claudius, and Nero. Following the suicide of Emperor Nero, there was a brief period of civil war. Between 68 and 69 A.D., the Roman Empire witnessed the successive rise and fall of Galba, Otho, Vitellius, and Vespasian, who was the first from the Flavian dynasty to rule. The Emperor Vespasian was followed by his sons Titus and Domitian. The unbalanced qualities of these monarchs that followed Augustus, indicated that the Romans had not yet discovered a method to choosing a capable ruler. Not until after the assassination of Domitian, did Rome turn their attention to this problem. The senate chose Nerva as the new Emperor and he established a plan that provided the empire with a succession of good rulers. The social, military, and political mayhem of the period had wide spread repercussions on the empire.
