1. The leader of the Gauls, who in B. C. 390 crossed the Apennines, took Rome, and overran the centre and the south of Italy. His real name was probably either Brenhin, which signifies in Kymrian "a king," or Bran, a proper name which occurs in Welsh history. (Arnold's Rome, vol. i. p. 524.) This makes it probable that he himself, as well as many of the warriors whom he led, belonged to the Kymri of Gaul, though the mass of the invaders are said by Livy (5.35) and by Diodorus (14.13) to have been Senones, from the neighbourhood of Sens, and must therefore, according to Caesar's division (B. G. 1.1) of the Gallic tribes, have been Kelts.

Little is known of him and his Gauls till they came into immediate contact with the Romans, and even then traditionary legends have very much obscured the facts of history.

It is clear, however, that, after crossing the Apennines (Diod. 14.113; Liv. 5.36), Brennus attacked Clusium, and unsuccessfully. The valley of the Clanis was then open before him, leading down to the Tiber, where the river was fordable; and after crossing it he passed through the country of the Sabines, and advanced along the Salarian road towards Rome. His army now amounted to 70,000 men. (Diod. 14.114.) At the Allia, which ran through a deep ravine into the Tiber, about 12 miles from the city, he found the Roman army, consisting of about 40,000 men, strongly posted. Their right wing, composed of the proletarians and irregular troops, was drawn up on high ground, covered by the ravine in front and some woody country on the flank; the left and centre, composed of the regular legions, filled the ground between the hills and the Tiber (Diod. 14.114), while the left wing rested on the river itself. Brennus attacked and carried this position, much in the same way as Frederick of Prussia defeated the Austrians at Leuthen. He fell with the whole strength of his army on the right wing of the Romans, and quickly cleared the ground. He then charged the exposed flank of the legions on the left, and routed the whole army with great slaughter. Had he marched at once upon the city, it would have fallen, together with the Capitol, into his hands, and the name and nation of Rome might have been swept from the earth. But he spent the night on the field. His warriors were busy in cutting off the heads of the slain (Diod. l.c.), and then abandoned themselves to plunder, drunkenness, and sleep. He delayed the whole of the next day, and thus gave the Romans time to secure the Capitol. On the third morning he burst open the gates of the city. Then followed the massacre of the eighty priests and old patricians (Zonar, 2.23), as they sat, each in the portico of his house, in their robes and chairs of state; the plunder and burning of all the city, except the houses on the Palatine, where Brennus established his quarters (Diod. 14.115); the famous night attack on the Capitol, and the gallant exploit of Manlius in saving it.

For six months Brennus besieged the Capitol, and at last reduced the garrison to offer 1000 pounds of gold for their ransom. The Gaul brought unfair weights to the scales, and the Roman tribune remonstrated. But Brennus then flung his broadsword into the scale, and told the tribune, who asked what it meant, that it meant " vae victim ease," that the weakest goes to the wall.

Polybius says (2.18), that Brennus and his Gauls then gave up the city, and returned home safe with their booty. But the vanity of the Romans and their popular legends would not let him so escape. According to some, a large detachment was cut off in an ambush near Caere (Diod. 14.117); according to others, these were none others than Brennus and those who had besieged the Capitol. (Strab. v. p.220.) Last of all, Camillus and a Roman army are made to appear suddenly just at the moment that the gold is being weighed for the Capitol, Brennus is defeated in two battles, he himself is killed, and his whole army slain to a man. (Liv. 5.49.)