Germanicus on his recall was in danger, while in Rome, of being made the head of a faction in antagonism to Drusus, the son of Tiberius. He was dispatched, however, with extraordinary powers, to take control of the East, where Piso, the governor of Syria, believed that he held his own appointment precisely that he might be a thorn in the side of Germanicus. The latter made a progress through Greece, settled affairs in Armenia and Parthia, and continued his journey to Egypt.
Piso's machinations, encouraged by the reports which reached him of the emperor's displeasure at the conduct of Germanicus, caused the gravest friction. Finally, on the return from Egypt through Syria, Germanicus became desperately ill. He declared his own belief that Piso and his wife had poisoned him; and, on his death, the rumour met general credence, though it was unsupported by evidence. Agrippina returned to Rome, bent on vengeance, and the object of universal sympathy. Piso attempted to make himself master of Syria, but failed to win over the legions, and then resolved to return to Rome and defy his accusers.
About this time Arminius was killed in attempting to make himself king. Shortly before, Tiberius had rejected with becoming dignity a rival chief's offer to poison the national hero of German independence.
On the arrival in Italy of Agrippina with the ashes of Germanicus, the popular and official expressions of grief and sympathy were almost unprecedented. This public display was not at all encouraged by Tiberius himself. Drusus was instructed to emphasize the fact that Piso must not be held either guilty or innocent, till the case had been sifted. Tiberius insisted that not he, but the senate, must be the judge; the case must be decided on its merits, not out of consideration for his own outraged feelings. Piso was charged with having corrupted the soldiery, levied war on the province of Syria, and poisoned Germanicus. All except the last charge were proved up to the hilt; for that alone there was no evidence. Piso, however, despaired, fearing less the ebullitions of popular wrath than the emotionless implacability of the emperor. He was found dead in his room; but whether by his own act or that of Tiberius, was generally doubted. The penalties imposed on his wife and son were mitigated by the emperor himself.
A number of notorious scandals at this period emphasise the degradation of morals and the disregard for the sanctity of the marriage tie in a society where children were regarded as a burden, in spite of official encouragement of the birth-rate. There was an instructive debate on a proposal that magistrates appointed to provinces should not take their wives with them.
Risings in Gaul of the Treveri and Aedui created much alarm in Rome; the composure of Tiberius was justified by their decisive suppression.
In Africa, Blæms successfully suppressed, though he did not finally curb, the brigand chief Tacfarinas, who had been building up a nomad empire of his own. It was under Dolabella, the successor of Blæms, that Tacfarinas was completely overthrown and slain.
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.