Tacitus (Marcus Claudius Tacitus)tăsˈĭtəs, d. 276, Roman emperor (275–76). An elderly senator with a reputation for honesty and vigor, he was chosen by the senate to succeed the murdered Aurelian. He failed to restore the glory of the senate, and after reigning only a few months he died when on campaign in Asia. He was almost certainly murdered. Probus succeeded him.