He was formally adopted by Augustus in AD 4. He then went into active service in northern Germany against the Marcomanni. Tiberius also succeeded in quelling formidable insurrections in Pannonia and Dalmatia, and finally in securing the frontier and taking vengeance upon the Germans, who had annihilated the army of the Roman general Publius Quintilius Varus (died AD 9) in the Teutoburger Wald in AD 9. Accompanied by Germanicus Caesar, who was his nephew and adopted son, Tiberius made two more marches into the heart of Germany, returning to Rome several years later to be accorded a triumph, the highest official tribute that was given to honor a victorious warrior.
When Augustus died at Nola, near Naples, in AD14, Tiberius, unopposed, succeeded to the throne. His reign was marked by revolts and rebellions in Pannonia, Germany, Gaul, and other parts of the empire. Domestically, the reign of Tiberius was at first beneficent. He improved the civil service, kept the army in strict discipline, and managed the finances with great ability and generosity; the provinces were better governed during his rule than ever before.
Gradually, however, a change took place, and the latter part of his reign was marked by a series of conspiracies and consequent executions. In AD26 Tiberius left Rome and withdrew to Campania, and the following year went to the island of Capreae (modern Capri), leaving Rome under the power of Lucius Aelius Sejanus (died AD31), the prefect of the Praetorian Guard. Finally realizing that Sejanus was trying to seize the imperial power, Tiberius had him and his supporters put to death in AD31. The emperor continued to live at Capreae until AD37.
He died on March 16, AD37, at Misenum, near Naples; some ancient historians believed he was smothered by the prefect of the Praetorian Guard. Tiberius’s coldness and reserve and his desire for economy in government rendered him unpopular with the people and, together with his supposed depravity, gave him a bad name in legend and history. Most modern scholars, however, reject the tales of his cruelty, hypocrisy, and debauchery that are related by the historians Tacitus and Suetonius. Tiberius seems to have been an able soldier and administrator who retained the republican form of government as much as possible.