Pausanias Description of Greece 10.21.4

[4] Meanwhile, the Athenians on the triremes, with difficulty and with danger, nevertheless coasted along through the mud that extends far out to sea, brought their ships as close to the barbarians as possible, and raked them with arrows and every other kind of missile. The Celts were in unspeakable distress, and as in the confined space, they inflicted few losses but suffered twice or four times as many, their captains gave the signal to retire to their camp. Retreating in confusion and without any order, many were crushed beneath the feet of their friends, and many others fell into the swamp and disappeared under the mud. Their loss in the retreat was no less than the loss that occurred while the battle raged.