The siege of Thala (108 BC) saw the Romans under Metellus capture the site of one of Jugurtha's treasuries, but without capturing the King or securing much of the treasure (Jugurthine War)
Over the winter of 109-108 BC Metellus attempted to defeat Jugurtha through treachery, winning over Bomilcar, one of his senior supporters. Bomilcar entered into a plot to overthrown the king with another senior Numidian, Nabdalsa, who had command of an independent military force. Nabdalsa then lost his nerve and didn't send his men on the agreed day. Bomilcar sent a letter to Nabdalsa to try and encourage him to stick to the plan, but almost inevitably this fell into the wrong hands and was taken to Jugurtha. Nabdalsa rushed to the king and threw himself on his mercy. Bomilcar was executed and Nabdalsa pardoned, but the plot undermined Jugurtha's confidence in his own men.
Metellus took advantage of Jugurtha's indecision to force him to accept battle. While the king was trying to decide what to do, and rapidly swapping between different plans, Metellus gathered his army and advanced towards Jugurtha's army, apparently catching the Numidians by surprise. Jugurtha didn't even have time to get his entire army into order of battle, and most of his troops fled without putting up any resistance. Only the troops nearest to Jugurtha fought well, but they were soon overwhelmed. The Romans captured a large number of Numidian standards and weapons, but most of Jugurtha's troops managed to flee to safety.
Jugurtha himself fled into the desert, and then reached the city of Thala, an isolated city separated from the nearest major river by fifty miles of desert (the city gained its water from several springs near the walls). Thala was where his children were being educated, and Sallust described it as a 'large and opulent city'. Before the siege it contained the largest part of Jugurtha's treasury.
Metellus decided to take the risk of attacking across the desert. He ordered those Numidians who had submitted to him to bring water to a pre-arranged camp. Most of the baggage was left at the nearest river and replaced with water containers. Local beasts of burden were also gathered up and loaded with water. Only ten days worth of provisions were carried.
The desert crossing went as planned, and the Romans and their new Numidian allies met up at the camp. However there was then such heavy rain that the Romans didn't actually need the water that had been brought for them, and preferred to use the rainwater, which they read as a sign of divine favour.
On the following day the Romans reached Thala. Jugurtha immediately fled from the city, taking his children and most of his treasure with him, leaving the inhabitants to defend the city and remaining treasure. According to Sallust after this Jugurtha never stayed in the same place for more than one day, to reduce the risk of being betrayed.
At Zama Metellus had attempted to assault the walls, and had been repulsed. At Thala he decided to conduct a more regular siege. The city was surrounded by a rampart and ditch and siege engines were constructed. The defenders held out for forty days, but eventually the Romans managed to capture the town. The surviving defenders retreated to the royal palace (presumably a defendible citadel), held one final feast and then set fire to the buildings, committing suicide and destroying what was left of the treasure.
By now Jugurtha was running out of Numidian supporters, and had to look further afield. He fled south into the lands of the Gaetulians, where he was able to raise troops. He also arranged an alliance with Bocchus, king of the Mauri, the kingdom in the north-western corner of Africa. This allowed him to continue fighting, despite the lack of local support.