The battle of Imbrinium (325 BC) was an early Roman victory in the Second Samnite War most famous for a violent dispute between the Dictator L. Papirius Cursor and his Master of the Horse.
At the start of the second full year of the war the Romans were faced with two enemies - the Samnites to their east and the Vestini, to the north-east of Rome on the Adriatic coast. The Senate decided to send armies against both of these enemies, and appointed the consul Junius Brutus Scaeva to command against the Vestini and L. Furius Camillus against the Samnites.
Furius Camillus led his army into Samnium, but soon fell ill and was forced to appoint a Dictator to take command of the army. He chose Lucius Papirius Cursor, one of the consuls of 326, with Quintus Fabius Maximus Rullianus as his Master of the Horse.
Soon after taking command Cursor was forced to return to Rome, according to Livy to have the auspices read for a second time. He left Rullianus in command, with clear orders not to leave the camp or to engage in a battle.
Perhaps inevitably Rullianus disobeyed this order. His scouts reported that the Samnites were vulnerable to attack. Rullianus led the army out of the camp, and into a district identified by Livy at Imbrinium, where he found a large Samnite army (the location of Imbrinium is unknown).
According to Livy the resulting battle was won by the Roman cavalry. After a series of unsuccessful charges L. Cominius, a military tribune, suggested that they should remove the bits from their horses and make a fresh charge. Rullianus took this advance, and the cavalry finally broke the Samnite lines. The infantry followed, and completed the victory. In keeping with his tendency to inflate Samnite casualties Livy records that they lost 20,000 men during this battle.
In the aftermath of this victory Rullianus seems to have gone out of his way to annoy the Dictator. The captured Samnite arms and armour should have formed part of Cursor's triumph, but Rullianus had them piled up on the battlefield and burnt. He then sent his dispatch reported the victory directly to the Senate, instead of to his superior. Cursor saw all of this as an attack on his authority, and in a fit of rage returned to the army, determined to arrest and execute Rullianus. After narrowly avoided execution at the camp, Rullianus escaped to Rome, where only the united appeal of almost the entire Roman people, from the Senate to the plebs, convinced Cursor to pardon him.
After this Cursor returned to the army, where according to Livy he fought two more battles. His treatment of Rullianus and his general attitude had made him unpopular in the army, and as a result the first battle ended in a draw. Only after taking some time to win his troops over was he able to win a clear victory, after which he returned to Rome to celebrate his triumph.