Plutarch Caius Marius 26

[1] At this time, however, they did not charge directly upon the Romans, but swerved to the right and tried to draw them along gradually until they got them between themselves and their infantry, which was drawn up on their left. The Roman commanders perceived the crafty design, but did not succeed in holding their soldiers back; for one of them shouted that the enemy was taking to flight, and then all set out to pursue them.

[2] Meanwhile the infantry of the Barbarians came on to the attack like a vast sea in motion. Then Marius, after washing his hands, lifted them to heaven and vowed a hecatomb to the gods; Catulus also in like manner lifted his hands and vowed that he would consecrate the fortune of that day. It is said, too, that Marius offered sacrifice, and that when the victims had been shown to him, he cried with a loud voice: Mine is the victory.

[3]
  After the attack had begun, however, an experience befell Marius which signified the divine displeasure, according to Sulla. For an immense cloud of dust was raised, as was to be expected, and the two armies were hidden from one another by it, so that Marius, when he first led his forces to the attack, missed the enemy, passed by their lines of battle, and moved aimlessly up and down the plain for some time. Meanwhile, as chance would have it, the Barbarians engaged fiercely with Catulus, and he and his soldiers, among whom Sulla says he himself was posted, bore the brunt of the struggle.

[4] The Romans were favoured in the struggle, Sulla says, by the heat, and by the sun, which shone in the faces of the Cimbri. For the Barbarians were well able to endure cold, and had been brought up in shady and chilly regions, as I have said. ¹ They were therefore undone by the heat; they sweated profusely, breathed with difficulty, and were forced to hold their shields before their faces. For the battle was fought after the summer solstice, which falls, by Roman reckoning, three days before the new moon of the month now called August, ² but then Sextilis.

[5] Moreover, the dust, by hiding the enemy, helped to encourage the Romans. For they could not see from afar the great numbers of the foe, but each one of them fell at a run upon the man just over against him, and fought him hand to hand, without having been terrified by the sight of the rest of the host. And their bodies were so inured to toil and so thoroughly trained that not a Roman was observed to sweat or pant, in spite of the great heat and the run with which they came to the encounter. This is what Catulus himself is said to have written ³ in extolling his soldiers.