Gaius Hostilius Mancinus

Gaius Hostilius Mancinus (fl. 140–135 BC) was a politician and general of the Roman Republic. He is mostly known for his defeat against the Numantines as consul in 137 BC and the humiliating treaty he signed afterwards in order to save his army.

Mancinus was born no later than 179 BC as a member of the plebeian gens Hostilia. He was elected as praetor around 140 BC, in which capacity he presided over a senatorial vote on a dispute between Narthakion and Melitaia, two cities in Thessaly allied to Rome. In 137 BC, he was elected consul and sent to command Roman forces in the Numantine War against the settlement of Numantia in Hispania. Following a series of defeats, he concluded a peace treaty with the Numantines, which preserved Numantia's independence and surrendered the Roman army's weapons and baggage to the Numantines.

In Rome, many senators were outraged by the treaty, notably Scipio Aemilianus, one of the most influential politicians of the period. During the ensuing debate, both the supporters and the critics of the treaty produced coinage and promulgated contradictory historical precedents as propaganda. The affair marked the beginning of Tiberius Gracchus' political career; he led the negotiations with the Numantines as a member of Mancinus' staff and supported the treaty in the senate. However, the senate ultimately rejected the treaty and, to avoid breaking Mancinus' religious oaths, surrendered him in chains to the Numantines. Mancinus won approval in Rome by making a speech before the senate in which he accepted his fate and affirmed his commitment to the oaths he had sworn.

However, as the Numantines refused to take him, Mancinus again returned to Rome, but was declared to have forfeited his citizenship and so to be ineligible to resume his place in the senate. Thanks to his courageous behaviour during the affair, he recovered some popularity and was able to have legislation passed restoring his citizenship. He was later successful in securing a second praetorship, restoring him to the senate.