 Pausanias describes how they used a tactic called "trimarcisia", where each cavalryman was supported by two mounted servants, who could supply him with a spare horse if he was dismounted, or take his place in the battle if he was killed or wounded, so the actual number of horsemen was in fact 61,200.The Greeks, mustered at Thermopylae under the Athenian general Calippus, learned that the Gauls had reached Phthiotis and Magnesia, sent their cavalry and light infantry to meet them at the river Spercheios and oppose their crossing.They broke down the bridges and camped on the bank, but that night Brennus sent 10,000 men to cross further downriver, where the river formed a marshy lake.