Hitherto the rule of Tiberius had been, on the whole, prosperous. But the ninth year marks the establishment of the ascendancy of Ælius Sejanus over the mind of the emperor, whereby his sway was transformed into a foul tyranny. Not of noble birth, Sejanus had neglected no means, however base, to secure his own favour with Tiberius and with the Prætorian Guard, of which he held the command. He was now determined to get rid of Drusus, the son of Tiberius, as the most dangerous obstacle to his ambitions. He accomplished his purpose by administering a poison, of which the operation was unsuspected till the facts were revealed many years later by an accomplice. Then the young sons of Germanicus became the accepted representatives of the imperial line, for the infant sons of Drusus died very shortly afterwards. Accordingly, Sejanus now directed his attacks against the more powerful persons who might be regarded as partisans of the house of Germanicus. Despite the multiplications of prosecutions, it is to be noted that it was still possible for a shrewd and tactful person, as exemplified by the career of Marcus Lepidus, to uphold the principles of justice and liberty without losing the favour of the emperor. Among other prosecutions, that of Cremutius, whose crime was that of praising the memory of Brutus and Cassius, demands attention, as the first of the kind. The ambitions of Sejanus received a check when he had the presumption to request Tiberius to grant him the hand of the widow of Drusus in marriage. In order the more surely to bring disgrace on the house of Germanicus, he now implanted in the mind of Agrippina a conviction that Tiberius intended to poison her. That such suspicions were mere commonplaces of that terrible time is well illustrated by the story. Incapable of hiding her feelings, the persistent gloom of her face and voice, and her refusal of proffered dishes as she sat near Tiberius at dinner, attracted his attention; to test her, he personally commended and pressed on her some apples; this only intensified her suspicions, and she gave them to the attendants untasted. Tiberius made no open comment, but observed to his mother that it would hardly be surprising should he contemplate harsh measures towards one who obviously took him for a poisoner. _III.--Morbid Tyrant and Dotard_ It was at this time that Tiberius withdrew himself from the capital, and took up his residence at a country seat where hardly anyone had access to him except Sejanus; whether at the favourite's suggestion or not is uncertain. The retreat finally selected was the island of Capræ.