The battle of the Caudine Forks (321 BC) was a humiliating defeat inflicted on the Romans by a Samnite army in the Apennine Mountains (Second Samnite War).
After winning a clear victory somewhere in Samnium in 322 BC the Romans rejected a Samnite peace offer, and prepared to resume their campaign in 321. The consuls for the year, Titus Veturius Calvinus and Spurius Postumius Albinus, took their combined army into Campania, and camped at Calatia, just to the east of Capua. Their combined army probably contained at least 18,000 men, if each consul led a single 4,500 strong legion, and at least 27,000 if they each commanded two legions, as was later the case.
The Samnites appointed Gavius Pontius as their captain-general for the year. According to Livy he decided to trick the consuls into a rash crossing of the Apennines. From his base close to Caudium (in the Apennine Mountains to the east of Calatia) he sent ten soldiers disguised as shepherds towards the Roman lines. When they fell into Roman hands they told the Romans that the city of Luceria in Apulia, which had only recently fallen into Roman hands, was being besieged. The consuls fell for this story, and decided to take the fastest route to Luceria, across the mountains.
Livy described the battlefield as being between 'two passes, deep, narrow, with wooded hills on each side'. A continuous chain of mountains extended from one pass to the other, hemming in a 'watered grassy plain through the middle of which the road goes'. Unfortunately this description doesn't match any of the routes across the Apennines, none of which have two narrow enough passes to fit with the rest of Livy's account of the battle.
According to Livy the Romans marched across the first pass, and through the grassy plain without noticing the Samnite forces hidden on the hills above them. When they reached the pass leading out of the plains they discovered that it was blocked by a barricade of felled trees with masses of rock piled against them. Only at this point did the Samnites reveal themselves on the hills above the valley. Realising they had been tricked, the Romans attempted to retrace their steps, only to find that the path had been blocked behind them. They were now trapped between two barricades, with enemy troops on the heights all around them.
The Roman army now sank into a pit of despondency, and couldn’t decide how to react. The consuls ordered the men to construct their normal marching camp, and something of a siege began. Gavius Pontius asked his father, Herennius, for advice on how to treat the Romans. His first response was to say let them go. When this advice was turned down he said 'kill them all'. When asked to explain the contradictory nature of his advice, his response was that the best response was to free the Romans, and use the good will generated to end the war on equal terms. If that wasn't acceptable, then the second best answer was to kill the entire Roman army, weakening the Republic and hopefully preventing them from launched any new invasion of Samnium for several years. Neither course was taken, and instead humiliating terms were imposed on the defeated Romans. As Herennius predicted this caused an outrage in Rome, and increased the Roman determination to fight on.
Other ancient sources suggest that a full scale battle took place somewhere in the hills near to Caudium, with the Samnites fighting from a strong position on the hills. Eventually the defeated Romans were forced to surrender.
The most famous incident of the battle took place after the Romans had surrendered. Gavius Pontius insisted that the entire army, from the two consuls down, should pass beneath the yoke (two spears thrust into the ground, with a third forming a crossbar), wearing only their tunics. This was seen as a major humiliation, signifying that the enemy soldier had been totally defeated, and was completely under the power of the victor.
The consuls were also forced to agree to a peace treaty. The Romans would withdraw their colonies from Samnium, including Cales and the colony at Fregellae that had helped trigger the entire war. After that relations between the two states would be governed by a fair treaty. The consuls and other officers present with the army agreed to this treaty, and then after passing under the yoke the defeated army returned to Rome.
The aftermath of this defeat is unclear. According to Livy the citizens of Rome refused to accept the treaty, and resumed the fight. A series of victories followed, including one at Luceria in 320 BC in which Gavius Pontius was himself captured and forced to pass under the yoke. This last element is almost certainly a later Roman fiction, although it is perfectly possible that the treaty was quickly disowned and some minor victories followed. Despite this, the memory of the Caudine Forks and the yoke remained part of Roman culture to the end of the Empire, becoming a symbol of humiliating failure.