In 391 a tribe of Italian Gauls, finding their territories too narrow for them, and possibly pressed by newcomers from the north, invaded Etruria, and attacked the city of Clusium. The people of Clusium sent envoys to Rome, asking for help.

The Romans did not think fit to send troops—it would have been a serious matter to levy an army for what may be called foreign service—but sent an embassy which was to represent to the Gauls that Clusium was a friendly city and must be left alone. The Gauls replied: "We have no wish to injure Clusium, but it has more land than it needs, while we have not enough. Let it give us a share, and we shall be content. If it refuses, stand by, and see whether we cannot make good our claims by force of arms."

The Roman ambassadors, three haughty young nobles—so the story runs—asked: "What are Gauls doing in Etruria? By what right do you come?" "By the right of our swords," was the answer. A battle followed, and the Roman ambassadors had the imprudence to take part in it. One of them struck down a Gallic chief, and was recognised as he stripped the fallen man of his arms. The Gauls at once drew off from the field. It was with Rome, not with Clusium, that they had thenceforward to deal.

They sent envoys demanding the surrender of the three men who had so grossly offended against the law of nations. The Senate asked counsel of the Priestly College which had to do with such matters. The college replied that the offenders ought to be given up. But the Senate hesitated. The three men belonged to what was then the most powerful family in Rome, the great Fabian House. Whether they referred the matter to the decision of the whole body of the people is not clear. In any case the people expressed its opinion in a way that could not be mistaken, for they elected the three envoys among the Military Tribunes for the next year. Tribuni Militares.")?>

The election took place, it is probable, late in the year. For this reason, and also, it is probable, because they thought it well to wait for reinforcements from kinsmen beyond the Alps, the Gauls did not immediately act on the challenge thus thrown down. It was not till the summer of the following year that they marched on Rome. They attacked no one on their way; their one thought seemed to be to avenge the insult which had been offered to them.

The Romans, on the other hand, were strangely insensible to their danger. They raised an army, indeed, partly of home levies, partly of allies, but no special care was taken to make it equal to the occasion; even in point of numbers it was insufficient. It was remembered afterwards that the religious ceremony with which it was usual to begin a campaign was omitted.

The army took up its position at a place about eleven miles from the city, where a small brook named the Allia fell into the Tiber. The battle that followed was soon over. The Gallic king, Brennus (Bran)  by name, charged the Roman line at the point where probably an attack was least expected, the rising ground occupied by the right wing.

The fury of the Gallic warriors carried all before them, much as some twenty centuries later Prince Charlie's Highlanders did at Prestonpans. Then they turned their victorious arms on the centre, which had been weakened to prolong the line, and on the left. There, too, the victory was rapid and complete.

The Romans fled precipitately across the river. Some were drowned; not a few were crushed to death by their comrades. The survivors made their way with headlong speed to Rome. The rout of Allia was rightly held to be one of the most disgraceful incidents in the Roman annals, and the day on which it happened (July 18th) was marked in the calendar as one of those on which no business could be transacted.

For two days the conquerors remained on the field of battle, celebrating their victory with revel, or, as the historian suggests, fearing that the speedy flight of the enemy concealed some deep design. On the third day they marched to Rome. They found the city deserted, with the exception of the Capitol, which was occupied by a garrison of picked men.

In the Forum, however, a strange spectacle met their eyes. There, seated on chairs of state, sat a company of venerable citizens. They were too old to be of any service in defending the Capitol; to fly from Rome seemed unworthy of their rank. Perhaps they might serve their country in the only way that was possible to them, by a death that would expiate its sin. The Gauls gazed on them with respectful astonishment. At last a barbarian ventured to stroke the beard of one of them. The old man, wroth at the familiarity, smote the man with his ivory staff. The Gaul, resenting the insult of a blow, slew him, and all the others met with the same fate.

Though the city was in the hands of the barbarians, Rome was not wholly lost. The Capitol was held by a strong garrison, too numerous, it may well be, for the room which it offered and for the store of provisions which it could hold: a large force had been collected at Veii, made up of fugitives from Allia, eager to wipe out their disgrace, and others who were longing for an opportunity to serve their country.

The invaders, on the other hand, were beginning to suffer in various ways. Rome, never a very healthy place, was particularly dangerous during the heat of summer. It was deserted at this season by all who could contrive to get away, and these strangers from a more temperate climate naturally suffered more than natives. Supplies began to run short. The stores found in the houses had been wastefully used; much had perished in the fires which broke out in the deserted city. The Gauls soon found themselves compelled to plunder the neighbouring country, and suffered much at the hands of enemies who were familiar with every spot, and were always on the watch to cut off stragglers.

Once indeed they were very near to a great success, nothing less than the capture of the Capitol itself. A messenger, despatched by the garrison to their countrymen at Veii, had contrived to make the expedition unobserved, but had left some trace of his movements. This the Gauls had not failed to detect, and they conceived the idea of a surprise.

The Romans had a very narrow escape. The sentinels were asleep; no such attacks had been made before; even the dogs were silent. So the Gauls were able to climb unobserved almost to the summit of the hill; but the geese which were penned in the temple of Juno heard their approach and began to cackle. The birds were sacred to the goddess, and though provisions had by this time run very short, they had not been touched, and their provender had been spared from the scanty rations of the men. This piety was now to be rewarded.

The clamorous birds roused a certain Marius Manlius from his slumbers; he hastily armed himself and ran to the edge of the cliff, just in time to hurl down the foremost of the attacking party. The enterprise, which could only have succeeded as a surprise, was abandoned, and the Capitol was saved. The incident was one of the most famous in Roman story. Virgil, in his description of the shield on which Vulcan pictured for Æneas the coming fortunes of his race, thus described it:—

Both sides were now growing weary of the conflict. The Gauls, suffering grievously from sickness and from scarcity, were longing to return to their native land; with the garrison things had come to an almost desperate pass. It was agreed that a large sum should be paid in gold, and that the invaders should depart. The agreement was carried out, and Rome was once more free.

Two picturesque stories, which are told of the last scene, may be repeated as they stand, without too precise an inquiry into their truth. According to one, when the gold was being weighed, Brennus, the Gallic king, threw his sword—the Gallic swords were notably long and heavy—into the scale in which lay the weights. When the Roman commissioners remonstrated, he cried out "Woe to the conquered!" (Vœ victis), and the Romans had to submit.

The other saved the Roman pride by representing that, just at the critical moment, Camillus, who had been duly appointed Dictator by the magistrates who were serving in the garrison of the Capitol, came up and drove the overbearing conquerors in headlong rout from the city. Rome had suffered the disgrace of having to bargain for her freedom, but not the crowning shame of having actually to buy off her conquerors.

The Gauls continued to be formidable enemies. From time to time during the next two centuries they appeared, carrying a sudden terror over the prosperous fields of Northern Italy—the Romans had a special word, indicative of sudden confusion and uproar (tumultus), to express their onslaughts—but they never again brought the great city so near to the brink of ruin.