 In 191 BC, he, along with his old associate Lucius Valerius Flaccus, was appointed as a lieutenant-general (legatus)under the Consul Manius Acilius Glabrio, who had been dispatched to Greece to oppose the invasion of Antiochus III the Great, King of the Seleucid Empire.In the decisive Battle of Thermopylae (191 BC), which led to the downfall of Antiochus, Cato behaved with his usual valor, and enjoyed good fortune.By a daring and difficult advance, he surprised and removed a body of the enemy's Aetolian auxiliaries, who were posted upon the Callidromus, the highest peak of the range of Mount Oeta.