ide. Agrippina, the
ambitious wife of Germanicus, believed that Tiberius from motives of
jealousy had been responsible for her husband's death. She openly
displayed her hostility to the princeps, and by plotting to secure the
succession for her own children, helped to bring about their ruin and her
own.

*The withdrawal of Tiberius from Rome, 26 A. D.* The decision of Tiberius
to leave Rome in 26 A. D. and take up his residence on the island of Capri
had important consequences. One was that the office of city prefect, who
was the representative of the princeps, became permanent. It was filled by
a senator of consular rank who commanded the urban cohorts and had wide
judicial functions.

*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.