*The plot of Seianus.* In the second place the absence of Tiberius gave his able and ambitious praetorian prefect Aelius Seianus encouragement and opportunity to perfect the plot he had formed to seize the principate for himself. He it was who concentrated the praetorian guard, now 10,000 strong, in their camp on the edge of the city, and paved the way for their baneful influence upon the future history of the principate. Having caused the death of Drusus, the son of Tiberius, by poison, in 23 A. D., he intrigued to remove from his path the sons of Germanicus, Drusus and Nero. They and their mother Agrippina were condemned to imprisonment or exile on charges of treason. In 31 A. D. Seianus attained the consulate and received proconsular _imperium_ in the provinces. He allied himself with the Julian house by his betrothal to Julia, the grand-daughter of Tiberius. But in the same year the princeps became aware of his plans. Tiberius acted with energy. Seianus and many of his supporters were arrested and executed. *The last years of Tiberius.* The discovery of Seianus’ treachery seems to have affected the reason of the aging princeps. His fear of treachery became an obsession. The law of treason (_lex de maiestate_) was rigorously enforced and many persons were condemned to death, among them Agrippina and her sons. The senators lived in terror of being accused by informers (_delatores_), and in their anxiety to conciliate the princeps they were only too ready to condemn any of their own number. The memory of his later years caused Tiberius to pass down in the traditions of the senatorial order, represented by Tacitus and Suetonius, as a ruthless tyrant, and to obscure his real services as a conscientious and economical administrator. His parsimony in expenditures of the public money won him unpopularity with the city mob, but was a blessing to the provincials to whose welfare Tiberius directed particular attention, while he vigorously protected them against the oppression of imperial officials. During his rule the peace of the empire was disturbed only by a brief rising in Gaul (21 A. D.) and a rather prolonged struggle with Tacfarinas, a rebellious Berber chieftain, in Numidia (17–24 A. D.). II. CAIUS CALIGULA, 37–41 A. D. *Accession.* Tiberius left as his heirs his adoptive grandson Caius, the sole surviving son of Germanicus, better known by his childhood name of Caligula, acquired in the camps on the Rhine, and his grandson by birth, Tiberius Gemellus. Upon Caius, the elder of the two, then twenty-five years of age, the Senate immediately conferred the powers of the principate. The resentment of the senators towards his predecessor found vent in refusing him the posthumous honor of deification. Caius adopted his cousin, but within a year had him put to death.