From our 21st century perspective, Ancient Rome's worst military defeats must include those that changed the path and progress of the mighty Roman Empire. From an ancient history standpoint, they also include those that the Romans themselves held up to later generations as cautionary tales, as well as the ones that made them stronger. In this category, the Roman historians included stories of losses made most painful by massive numbers of deaths and capture, but also by humiliating military failures. Here is a list of some of the worst defeats in battle suffered by the ancient Romans, listed chronologically from the more legendary past to the better-documented defeats during the Roman Empire.

01 of 08 Battle of the Allia (ca. 390–385 BCE) De Agostini / Icas94 / Getty Images The Battle of the Allia (also known as the Gallic Disaster) was reported in Livy. While at Clusium, Roman envoys took up arms, breaking an established law of nations. In what Livy considered a just war, the Gauls took revenge and sacked the deserted city of Rome, overpowering the small garrison on the Capitoline and demanding a large ransom in gold. While the Romans and Gauls were negotiating the ransom, Marcus Furius Camillus turned up with an army and ousted the Gauls, but the (temporary) loss of Rome cast a shadow over Romano-Gallic relations for the next 400 years.​

02 of 08 Caudine Forks (321 BCE) Getty Images / Nastasic Also reported in Livy, the Battle of Caudine Forks was a most humiliating defeat. The Roman consuls Veturius Calvinus and Postumius Albinus decided to invade Samnium in 321 BCE, but they planned poorly, choosing the wrong route. The road led through a narrow pass between Caudium and Calatia, where the Samnite general Gavius Pontius trapped the Romans, forcing them to surrender. In order of rank, each man in the Roman army was systematically subjected to a humiliating ritual, forced to "pass under the yoke" (passum sub iugum in Latin), during which they were stripped naked and had to pass under a yoke formed from spears. Although few were killed, it was a notable and conspicuous disaster, resulting in a humiliating surrender and peace treaty.

03 of 08 Battle of Cannae (during the Punic War II, 216 BCE) Nastasic / Getty Images Throughout his many years of campaigns in the Italian peninsula, the leader of the military forces at Carthage Hannibal inflicted crushing defeat after crushing defeat on the Roman forces. While he never marched on Rome (seen as a tactical error on his part), Hannibal did win the Battle of Cannae, in which he fought and defeated Rome's largest field army. According to writers such as Polybius, Livy, and Plutarch, Hannibal's smaller forces killed between 50,000 to 70,000 men and captured 10,000. The loss forced Rome to rethink every aspect of its military tactics completely. Without Cannae, there would never have been the Roman Legions.

04 of 08 Arausio (during the Cimbric Wars, 105 BCE) De Agostini / R. Ostuni / Getty Images The Cimbri and Teutones were Germanic tribes who moved their bases between several valleys in Gaul. They sent emissaries to the Senate in Rome requesting land along the Rhine, a request which was denied. In 105 BCE, an army of the Cimbri moved down the eastern bank of the Rhone to Aruasio, the furthest Roman outpost in Gaul. At Arausio, the consul Cn. Mallius Maximus and proconsul Q. Servilius Caepio had an army of about 80,000 and on October 6, 105 BCE, two separate engagements occurred. Caepio was forced back to the Rhone, and some of his soldiers had to swim in full armor to escape. Livy cites the claim by the annalist Valerius Antias that 80,000 soldiers and 40,000 servants and camp followers were killed, though this is probably an exaggeration.

05 of 08 Battle of Carrhae (53 BCE) Hulton Archive / Getty Images In 54–54 BCE, the Triumvir Marcus Licinius Crassus let a reckless and unprovoked invasion of Parthia (modern Turkey). The Parthian kings had gone to considerable lengths to avoid a conflict, but political issues in the Roman state forced the issue. Rome was led by three competing dynasts, Crassus, Pompey, and Caesar, and all of them were bent on foreign conquest and military glory. At Carrhae, the Roman forces were crushed, and Crassus was killed. With the death of Crassus, a final confrontation between Caesar and Pompey became inevitable. It wasn't the crossing of the Rubicon that was the death knell of the Republic, but the death of Crassus at Carrhae.

06 of 08 The Teutoburg Forest (9 CE) Kean Collection / Getty Images In the Teutoburg Forest, three legions under the governor of Germania Publius Quinctilius Varus and their civilian hangers-on were ambushed and virtually wiped out by the supposedly friendly Cherusci led by Arminius. Varus was reportedly arrogant and cruel and pursued heavy taxation on the Germanic tribes. The total Roman losses were reported to be between 10,000 and 20,000, but the disaster meant that the frontier coalesced on the Rhine rather than the Elbe as planned. This defeat marked the end of any hope of Roman expansion across the Rhine.

07 of 08 Battle of Adrianople (378 CE) DEA / A. DE GREGORIO / Getty Images In 376 CE, the Goths beseeched Rome to allow them to cross the Danube to escape from the deprivations of Atilla the Hun. Valens, based at Antioch, saw an opportunity to gain some new revenue and hardy troops. He agreed to the move, and 200,000 people moved across the river into the Empire. The massive migration, however, resulted in a series of conflicts between the starving Germanic people and a Roman administration which would not feed or disperse these men. On August 9, 378 CE, an army of Goths led by Fritigern rose and attacked the Romans. Valens was killed, and his army lost to the settlers. Two-thirds of the Eastern army were killed. Ammianus Marcellinus called it "the beginning of evils for the Roman empire then and thereafter."