The Lives of the Caesars by Suetonius

Tiberius 52, 53

LII. He had a father's affection neither for his own son Drusus nor his adopted son Germanicus, being exasperated at the former's vices; and, in fact, Drusus led a somewhat loose and dissolute life. Therefore, even when he died, Tiberius was not greatly affected, but almost immediately after the funeral returned to his usual routine, forbidding a longer period of mourning. Nay, more, when a deputation from Ilium offered him somewhat belated condolences, he replied with a smile, as if the memory of his bereavement had faded from his mind, that they, too, had his sympathy for the loss of their eminent fellow-citizen Hector. As to Germanicus, he was so far from appreciating him, that he made light of his illustrious deeds as unimportant, and railed at his brilliant victories as ruinous to his country. He even made complaint in the Senate when Germanicus, on the occasion of a sudden and terrible famine, went to Alexandria without consulting him. It is even believed that he caused his death at the hands of Gnaeus Piso, governor of Syria, and some think that when Piso was tried on that charge, he would have produced his instructions, had not Tiberius caused them to be taken from him when Piso privately showed them, and the man himself to be put to death. Because of this the words, "Give us back Germanicus," were posted in many places, and shouted at night all over the city. And Tiberius afterwards strengthened this suspicion by cruelly abusing the wife and children of Germanicus as well.

LIII. When his daughter-in-law Agrippina was somewhat outspoken in her complaints after her husband's death, he took her by the hand and quoted a Greek verse, meaning "Do you think a wrong is done you, dear daughter, if you are not empress?" After that he never deigned to hold any conversation with her. Indeed, after she showed fear of tasting an apple which he handed her at dinner, he even ceased to invite her to his table, alleging that he had been charged with an attempt to poison her; but as a matter of fact, the whole affair had been prearranged, that he should offer her the fruit to test her, and that she should refuse it as containing certain death. At last, falsely charging her with a desire to take refuge, now at the statue of Augustus and now with the armies, he exiled her to Pandataria, and when she loaded him with reproaches, he had her beaten by a centurion until one of her eyes was destroyed. Again, when she resolved to die of starvation, he had her mouth pried open and food crammed into it. Worst of all, when she persisted in her resolution and so perished, he assailed her memory with the basest slanders, persuading the Senate to add her birthday to the days of ill omen, and actually taking credit to himself for not having had her strangled and her body cast out on the Stairs of Mourning. He even allowed a decree to be passed in recognition of this remarkable clemency, in which thanks were offered him and a golden gift was consecrated to Jupiter of the Capitol.