Tiberius Sempronius (taɪˈbɪərɪəs sɛmˈprəʊnɪəs). ?163–133 bc, and his younger brother, Gaius Sempronius (ˈɡaɪəs), 153–121 bc, known as the Gracchi. Roman tribunes and reformers. Tiberius attempted to redistribute public land among the poor but was murdered in the ensuing riot. Violence again occurred when the reform was revived by Gaius, and he too was killed