Tiberius' brother Gaius was elected tribune in 123 BC. Gaius Gracchus' ultimate goal was to weaken the senate and to strengthen the democratic forces. In the past, for example, the senate would eliminate political rivals either by establishing special judicial commissions or by passing a senatus consultum ultimum ("ultimate decree of the senate"). Both devices would allow the Senate to bypass the ordinary due process rights that all citizens had. Gaius outlawed the judicial commissions, and declared the senatus consultum ultimum to be unconstitutional. Gaius then proposed a law which would grant citizenship rights to Rome's Italian allies. This last proposal was not popular with the plebeians and he lost much of his support. He stood for election to a third term in 121 BC, but was defeated and then murdered by representatives of the senate with 3,000 of his supporters on Capitoline Hill in Rome. Though the senate retained control, the Gracchi had strengthened the political influence of the plebeians.

In what year was Gaius elected to office?