§1.23.1Postridie eius diei, quod omnino biduum supererat, cum exercitui frumentum metiri oporteret, et quod a Bibracte, oppido Haeduorum longe maximo et copiosissimo, non amplius milibus passuum XVIII aberat, rei frumentariae prospiciendum existimavit; itaque iter ab Helvetiis avertit ac Bibracte ire contendit.
On the following day, because in all only two days remained until the time when they had to measure out grain to the army, and because he was not more than eighteen miles from Bibracte, by far the largest and most well-provisioned town of the Haedui, he thought that he must provide for the grain supply; therefore, he turned his route away from the Helvetii and hastened to go to Bibracte.
§1.23.2Ea res per fugitivos L. Aemilii, decurionis equitum Gallorum, hostibus nuntiatur.
This event was reported to the enemy through deserters of Lucius Aemilius, a decurion of the Gallic cavalry.
§1.23.3Helvetii, seu quod timore perterritos Romanos discedere a se existimarent, eo magis quod pridie superioribus locis occupatis proelium non commisissent, sive eo quod re frumentaria intercludi posse confiderent, commutato consilio atque itinere converso nostros a novissimo agmine insequi ac lacessere coeperunt.
The Helvetii, either because they thought that the Romans, terrified by fear, were retreating from them—all the more because on the previous day, although they had occupied the higher ground, they had not joined battle—or because they trusted that the Romans could be cut off from their grain supply, changed their plan, reversed their route, and began to pursue and harass our men from the rear.