The battle of Tarracina of 314 BC was a Roman victory that restored the situation after the Samnite victory at Lautulae in the previous year, and that eliminated a Samnite threat to Latium.
Diodorus Siculus provides a short summary of the campaign. The Samnites were advancing through Campania, attacking Roman allies. An army led by unnamed Roman consuls advanced towards them, and the two armies met near the port city of Tarracina. The Romans lifted a possible siege of the city, and then a few days later a hard-fought battle took place. The Romans were victorious, and killed more than 10,000 Samnites, although they also suffered heavy casualties.
Livy gives more detail, at least assuming that the two accounts refer to the same battle. The consuls M. Poetilius and Caius Sulpicius Longus had taken over the Roman army at the start of their year. They had then taken the city of Sora, and captured the three key cities in Ausonia. While the Romans were campaigning to their west the Samnites were active in Apulia, briefly capturing Luceria, but news of a political controversy at Rome and a possible revolt in Campania convinced them to move west. The Samnite army moved to Caudium, from where they could threaten Capua. The consuls responded by moving to the other end of a pass leading to Caudium (perhaps the site of the defeat at the Caudine Forks), and a stalemate developed, with neither side willing to risk moving.
It was the Samnites who made the first move, advancing around the Romans into a flat district of Campania. The two armies were now close to each other, and a series of cavalry skirmishes followed. These convinced the consuls that they could risk offering battle.
The Romans drew up with their legions in the centre and their cavalry on the flanks, as normal, but the cavalry had orders to concentrate on defending the Roman camp. Poetilius commanded the Roman left, which was in their normal close formation, while Sulpicius commanded the right, which was in a more open formation, matching the Samnites who were arrayed in thin extended ranks, apparently to stop the Romans outflanking them, and suggesting that they were outnumbered.
The battle began on the Roman left. Poetilius called up the infantry reserves, and charged with his entire wing. The Samnite infantry was shaken, and their cavalry was forced to come to their rescue. This dragged in the Roman cavalry, and for some both sides were in some confusion, until eventually the Samnites were forced back.
Sulpicius and his cavalry left the right wing when the fighting began on the left. While he was away the Samnites pushed the Roman infantry back, and were threatening to force them off the battlefield. Sulpicius returned just in time to save the situation, and the Samnites were soon pushed back.
The Romans now had the advantage all along the line, and Samnite resistance began to crumble. According to Livy 30,000 Samnites were either killed or taken prisoner, but like most of his casualty figures from this period that has to be a massive exaggeration. The survivors from the Samnite army retreated to Maleventum, later renamed Beneventum, while the Romans moved off to besiege Bovianum.