Titus Livius (Livy), The History of Rome, Book 5
Benjamin Oliver Foster, Ph.D., Ed.

37. Now that so heavy a calamity drew towards,-such is the blindness Fortune visits on men's minds when she would have her gathering might meet with no check, —that state which against the Fidenates and Veientes and other neighbouring tribes had on many occasions resorted to the last expedient and named a dictator —that [2] state, I say, though now an enemy never yet seen or heard of was rousing up war from the ocean and the remotest corners of the world, had recourse to no unusual authority or help. [3] The tribunes whose rashness had brought on the war were in supreme command; they conducted the levy with no greater care than had usually been employed in preparing for ordinary campaigns,¹ and even disparaged the rumoured seriousness of the danger. [4] The Gauls, meanwhile, on learning that honours had actually been conferred on men who had violated the rights of mankind and that their embassy had been made light of, were consumed with wrath (a passion which their race is powerless to control), an straightway catching up their standards, set their column in rapid motion. [5] As they marched swiftly and noisily on, the terrified cities armed in haste, and the peasants fled; but they signified with loud cries, wherever they came, that Rome was their goal, and their horse and foot in an extended line covered a vast tract of ground. [6] Yet, though rumour and the report of the Clusini preceded them, and [p. 129]after that successive messages from other peoples,² the utmost consternation was wrought in Rome by the enemy's swiftness, which was [7??] such that the army, albeit levied as it were en masse and hurriedly led out, barely covered eleven miles before confronting him, at the point where the river Allia descends in a very deep channel from the Crustuminian mountains, and mingles, not far south of the highway, with the waters of the Tiber.³ [8] The Gauls had already overrun all the ground in front and on both sides, and —the race being naturally given to vainglorious outbursts —their wild songs and discordant shouts filled all the air with a hideous noise.