The siege near the Muluccha River (106 BC) saw Marius besiege and capture one of Jugurtha's last fortresses, almost at the western border of Numidia.
Most of the previous campaigns of the Jugurthine War had taken place in the east of the country, the area closest to the Roman province of Africa. The main recorded event of Marius's first year in command was a siege of Capsa, in the far south-eastern corner of the country. After taking and destroying this city, Marius then advanced across the country. Some towns were captured after a brief fight, but most were abandoned before he arrived, and burnt. Jugurtha had already lost most of his Numidian supports, and was relying on an army of Gaetulians under his own command and his ally King Bocchus of the Mauri, but Bocchus proved unwilling to fight the Romans at this stage of the war, leaving Jugurtha unable to protect his kingdom.
Marius's campaign eventually brought him to the western end of Numidia, close to the River Muluccha, which formed the border with Mauritania. Just to the east of the river Jugurtha had a small fort on top of a high rocky hill. This could only be approached along one narrow path, with steep drops on either side. The fortress had a strong garrison, was well stocked with food and arms and there was a spring within the fort. The surrounding area wasn't suitable for siege works. Jugurtha had placed some of his remaining wealth in the fort.
Unsurprisingly this attracted Marius's attention. He constructed vineae (simple shelters to protect the troops) but these were destroyed by fire or stones thrown down from the fort. The fortress was so strong that Marius considered abandoning the siege, but according to Sallust he was saved by a lucky chance. One of his Ligurian auxiliaries, while exploring the side of the fort furthest from the Roman camp, noticed some edible snails on the rocks. As he collected the snails he ended up climbing further and further up the hill and eventually reached almost to the top. Once there he climbed up a handy oak tree that allowed him to see into the fort. He then returned to ground level, carefully noted the route back, and then reported to Marius.
Marius sent some of his men to examine the same route, but they couldn't agree if it was a possible route. Marius decided that it was worth trying out the new route. He selected five of his most nimble trumpeters, and gave them a guard of four centurions (probably but not certainly accompanied by some of their men). The Ligurian was to lead the party. Their role was to provide a distraction in the rear of the defenders during Marius's next attack.
On the day of the attack the Ligurian successfully led his men to the top of the hill on the far side to the main attack. Marius organised another full scale attack, forming his men into a testudo and advancing to the foot of the walls, while his missile troops harassed the defenders. The Numidians came out of the fort to attack the Romans, and were heavily engaged in the battle when the Roman trumpets were heard in their rear. The Numidians turned and fled back into the fort, with the Romans pressing them closely. The Romans wounded and killed a large number of the defenders.
Sallust's account ends with the Romans fighting to be first to reach the wall, and then moves onto an account of Sulla's arrival at the camp, but presumably the fort fell to the Romans. Bocchus had failed to provide any assistance to Jugurtha during this siege, and was clearly an unreliable ally, but Jugurtha was desperate. He offered to give Bocchus one third of Numidia either if the Romans were driven out of Africa or if the war ended without Jugurtha losing any territory. This finally convinced Bocchus to fight, and he took part in the last major battles of the war, the first battle of Cirta and second battle of Cirta.