When Tiberius died on 16 March 37 AD, his estate and the titles of the principate were left to Caligula and Tiberius's own grandson, Gemellus, who were to serve as joint heirs. Although Tiberius was 77 and on his death bed, some ancient historians still conjecture that he was murdered. Tacitus writes that Macro smothered Tiberius with a pillow to hasten Caligula's accession, much to the joy of the Roman people, while Suetonius writes that Caligula may have carried out the killing, though this is not recorded by any other ancient historian. Seneca the Elder and Philo, who both wrote during Tiberius's reign, as well as Josephus, record Tiberius as dying a natural death. Backed by Macro, Caligula had Tiberius's will nullified with regard to Gemellus on grounds of insanity, but otherwise carried out Tiberius's wishes.