The battle of Mount Gaurus, 343 B.C., was the opening battle of the First Samnite War (343-341 B.C.), and was a hard fought Roman victory.
The war was triggered by a Samnite attack on the Sidicini. The Sidicini received help from a northern Campanian league led by Capua, but their new allies suffered one defeat in Sidicini and a second outside Capua, which was then besieged. The Campanians called for help from Rome, and after some debate the Republic decided to intervene.
Both of the consuls for 343 led armies against the Samnites. Valerius Corvus led the army that was sent into Campania. He marched south to Mount Glaurus, to the west of Naples, and some way to the south of Capua, where he was faced with a strong Samnite army.
After a few days of skirmishes Valerius decided to risk a full scale battle. This was the first clash between the Romans and the Samnites, and both sides showed a great deal of determination. The battle began with a lengthy clash between the infantry, which was inconclusive. Valerius must have pulled his infantry back a short distance, for he then launched a cavalry charge in an attempt to break the enemy lines. This also failed, and the Roman cavalry was forced to turn around between the lines and retreat.
After the failure of the cavalry charge Valerius dismounted, and led a fresh infantry assault. Even this failed to break the Samnite lines, and it only as night approached did they begin to fall back (according to Livy the Samnite retreat began because the 'eyes of the Romans looked like fire and their faces and expression like those of madmen').
On the night after the battle the Samnites withdrew from the area, and on the following day the Romans occupied their camp. Livy doesn't give any casualty figures, perhaps suggesting that the Samnites didn't suffer very heavy losses during the battle. They were certainly able to form a new army in Campania later in the same year, suffering a second defeat against Valerius at Suessula.