The Roman legions in the north mutinied as they had not been paid and Tiberius did not issue instructions on that matter. Germanicus, a general, and Dusus (Tiberius’ son) were sent with a small force to put down the rebellion. Germanicus led the legions on a campaign across the river Rhine and said that the war booty would be their bonus. The campaign was victorious and was successful in quelling the mutiny. In 18 AD Germanicus was given the command of the Roman troops in the eastern part of the Roman Empire. However he died one year later and accused Piso, the governor of Syria, of poisoning him while he was dying. Piso was tried, but he threatened to implicate Tiberius. Since the senate was hostile to him, he committed suicide. . In 23 AD his son Drusus, with whom Tiberius shared his tribunician authority, mysteriously died.
From then on Tiberius, tired of politics, started to make longer and longer annual stays at the island of Capri, off Naples. In 26 AD he retired on this island. He increasingly relied on Lucius Aelius Sejanus to run the governance of the empire and with his withdrawal to Capri Sejanus came to control the state machinery. Tiberius called him his socius laborum (partner in my labours). Sejanus plotted to overthrow Tiberius. The plot was discovered and in 31 AD Tiberius ordered his execution. The senate also persecuted several of Sejanus colleagues. Tiberius now embarked on a series of treason trials. It was said that everyone who had some connection with Sejanus and members of families who had ties with the rival Julian family were tired and executed. This led to a view that the last years of Tiberius’ reign as tyrannical.
This view has been challenged by several historians. They note that throughout Tiberius’ reign only 52 people were charged with treason and that only half of them were convicted. They also claim that many of the trials were more down to the zeal of the senate, rather than Tiberius himself.