The siege of Capsa (107 BC) was Marius's first major military success in Numidia, but although it helped him conquer the south-east of the kingdom it failed to bring an end to the war any nearer (Jugurthine War).
Marius arrived in Numidia with a new army in 107 BC. Many of his new troops were entirely inexperienced, so he began a series of low risk raids into prosperous parts of the kingdom, capturing weakly defended places and winning a number of minor encounters. At the start of the campaign he faced two opponents - King Jugurtha, with an army of Gaetulians, and King Bocchus of the Mauri - but once the fighting began the two kings separated, and Bocchus didn't play any further part in the year's fighting. Jugurtha also refused to risk a battle, frustrating Marius.
Marius decided to force Jugurtha into action by attacking Capsa, a sizable city in the south-east of the city. Sallust reports that he was also motivated by a desire to equal the achievements of his predecessor Metellus, who had captured the equally inaccessible city of Thala in the previous year. Capsa (modern Gafsa) was surrounded by deserts, getting its water from a single spring within the city and from rainwater.
Marius planned the advance towards Capsa very carefully. He gathered a sizable amount of cattle, which he distributed as supplies during the six day march to the River Tana. The men were ordered to make new water bottles from the hides after they had eaten the cattle.
After reaching the Tana, Marius began a series of night marches. Well before dawn on the third night he reached a location two miles from Capsa, where he waited for daybreak. The defenders of Capsa had no idea that he was nearby, and were unable to defend themselves when Marius sent his cavalry and light infantry to capture the city gates. The surprised defenders attempted to surrender, but Marius refused to accept their submission. Instead he had the city burned down, the adults killed and the rest sold into slavery, with the profits distributed amongst his soldiers. Sallust describes this as against the usages of war, but also as being carried out because Capsa was so difficult to reach that it would be hard to return if the city was went back to Jugurtha.
After the destruction of Capsa, Marius returned to the heart of the kingdom and continued to attack those cities hold out for Jugurtha. Most were deserted before he arrived, as news spread of the massacre at Capsa. This campaign may have taken place late in 107 BC or during 106 BC. The next significant event reported by Sallust is the siege of a fortress near the Muluccha River, in the far west of Numidia, which must have happened in 106 BC.