The battle of Canusium (89 BC) was a series of conflicts that saw the Romans under Gaius Cosconius defeat the Samnites in Apulia and regain control of much of the area (Italian Social War).
In 90 BC the Italian leader Vidacilius had campaigned in Apulia, and had won over Canusia, Venusia and many other towns. Some came over willingly and others had to be besieged, although we don’t know which. Vidacilius was then drawn north in an attempt to save his home town of Asculum in Picenum, where he committed suicide.
In 89 BC the Roman praetor Gaius Cosconius campaigned in Apulia. His first recorded success came at Salapia, a town on a coastal lagoon just to the west of the Aufidus River. He then moved east and accepted the surrender of Cannae, a few miles inland on the Aufidus, and famous as the site of one of Rome's worst defeats. From Cannae he moved south to Canusium (modern Canosi di Puglia, just to the east of the river), and besieged the city.
The Samnites sent an army under the otherwise unknown general Trebatius to lift the siege. At first Trebatius was succesful, and after a costly battle Cosconius was forced to retreat north to Cannae. Trebatius followed him, and soon the two armies were only separated by a river (probably the Aufidus, in which case Cosconius had crossed the river in the aftermath of his defeat).
Something of a standoff must have developed, before Trebatius sent a messenger to Cosconius asking him to either cross the river, or to withdraw so that the Samnites could cross. Cosconius agreed to withdraw a short distance, but then attacked while Trebatius was in the middle of crossing the river. This must have produced a rather one-sided battle, and Appian reports that Trebatius lost 15,000 men. He escaped from the battle, and took refuge in Canusium with the survivors.
This gave Cosconius the freedom to overrun most of Apulia. He overran the territory of Larinum (just to the west of Apulia, in the coastal part of Samnium), Venusia (south of Canusium) and Asculum (modern Ascoli Satriano, to the west of Canusium, not to be confused with Asculum in Picenum, the site of a long siege during the war) , and received the surrender of the Poediculi (in eastern Apulia). By now most of the Italian rebels had surrendered, and only the Samnites and Lucanians were still holding out.
The final recorded battle of the war came at the Teanus River, probably close to Teanum Apulum, at the western edge of Apulia, probably in the following year. The Samnite leader Quintus Poppaedius Silo was killed in this battle, possibly while attempting to rescue Trebatius.
This wasn't Cosconius's only success during the war. The periochae of Livy reports that he killed the Samnite leader Marius Egnatius in battle, probably in the same year.