*Agrippina the younger.* In 49 A. D. the plot of Messalina, the third wife of Claudius, and her lover Gaius Silius, to depose the princeps in favor of Silius, endangered the power of the trio Pallas, Narcissus and Callistus. It was Narcissus who revealed the conspiracy to Claudius, secured his order for the execution of Messalina, and saw that it was carried into effect. But it was Pallas who induced the princeps to take as his fourth wife his own niece Agrippina, whose ambitions were to prove his ruin. *Death of Claudius.* By Messalina Claudius had a son Britannicus and a daughter Octavia, but Agrippina determined to secure the succession for Domitius, her son by her previous husband Lucius Domitius Ahenobarbus. In 50 A. D., Domitius was adopted by Claudius as Nero Claudius Caesar. The following year he received the _imperium_, and was thus openly designated as the future princeps. In 53 A. D. Nero was married to Octavia and a year later Claudius died, poisoned, as all believed, by Agrippina, who feared that further delay would endanger her plans. IV. NERO, 54–68 A. D. *The quinquennium Neronis.* Agrippina had previously made sure of the support of the praetorians, and so the appointment of Nero to the principate transpired without opposition. The first five years of his rule were noted as a period of excellent administration. During that time his counsels were guided by the praetorian prefect, Afranius Burrus from Narbonese Gaul, and by Lucius Annaeus Seneca, the famous writer and orator from Spain, whom Agrippina had appointed as his tutor in 49 A. D. *Fall of Agrippina.* This epoch is also characterized by the attempt of Agrippina to act as regent for her son and retain the influence she had acquired during the later years of the life of Claudius. But in this she was opposed both by Nero himself and his able advisors. In 55 A. D. Nero caused his adoptive brother Britannicus to be poisoned, through fear that he might prove a rival. Finally, under the influence of his mistress, Poppaea Sabina, the wife of Titus Salvius Otho, he had Agrippina murdered (59 A. D.). Thereupon he divorced Octavia, who was later banished and put to death, and married Poppaea.