In 118 BC the king of Numidia, Micipsa, died, leaving the crown to his young sons Hiempsal and Adherbal jointly with a much older nephew, Jugurtha, who was an experienced soldier.
Jugurtha arranged the assassination of Hiempsal, whilst Adherbal fled for his life and appealed to the senate.
The senate decided to send a commission to Numidia to divide he kingdom between the two claimants. Jugurtha appeared to bribe the commission's leader, Opimius, who returned to Rome a richer man, after awarding the greater and wealthier part of Numidia to Jugurtha. Though this was not enough for the ambitious Jugurtha who then marched on the territory of Adherbal and had him murdered, too.
Rome was outraged. Rome's judgement had simply been swept aside. Under the consul L Calpurnius Bestia troops were sent to Numidia to deal with the usurper. But the campaign was ineffective from the start, the Roman heavy infantry struggling to make any impression on the nimble Numidian horsemen.
Back in Rome eventually the comitia tributa to halt the campaign to have Jugurtha summoned to Rome to give evidence against any senators who were alleged to have accepted bribes from him. For this he was assured safe-conduct, meaning he was promised no to be charged or in any way harmed himself. But, once Jugurtha had arrived in Rome, these legal proceedings were stopped by a Tribune of the People who sought to avoid a political scandal.
So effective were Jugurtha's methods that even while he was in Rome he had another cousin murdered in the city.
This was too much, and he was ordered to depart.
'A city for sale !' he is said to have sneered as he left.
More troops were now sent to Africa to deal with the usurper. though the campaign was so ill managed that a commission of inquiry was held, which revealed such dire scandals of widespread bribery and corruption that three ex-consuls, one being Opimius, retired into exile. Instead Quintus Metellus and Gaius Marius, both known not only for their ability as well as their for being virtually incorruptible, were sent out to Africa to take command of the troops (109 BC).
Metellus was a good soldier who conducted his campaigns with skill and vigour, but Jugurtha, a master of the arts of guerilla warfare, held out against him. Marius, a better soldier than Metellus, returned to Rome to stand for the consulship, claiming that if the command were given to him the war would be ended at once.
In fact, by the time he returned to Africa as consul to supersede Metellus, it appeared that Jugurtha was beaten. Metellus went home bitterly disappointed at having had his victory snatched from him. But Jugurtha was not finished yet.
Marius could not catch him, and he found a dubious ally or protector in his neighbour Bocchus, king of Mauretania. Finally it was the diplomatic skill of the quaestor Lucius Cornelius Sulla that induced Bocchus to betray Jugurtha to the Romans and to a miserable death at Rome. But the conquest was credited to Marius.