The spring of 191 BC saw the Macedonians enter the war against the Aetolian League – they operated independently of the Romans – and occupy a number of towns in Thessaly. Antiochus moved on Acarnania, but was forced to withdraw when he heard of the incursion into Thessaly. By the time the consul Glabrio reached Thessaly, towns simply surrendered without a fight. Antiochus, receiving no reinforcements and heavily outnumbered by the Roman coalition, was forced to choose between retreat or doing battle where the coalition's numerical superiority would be minimised. He chose Thermopylae. The resulting battle was such an overwhelming defeat for Antiochus that he immediately fled Greece for Ephesus. Less than six months had elapsed from his arrival in Demetrias. With the Roman victory there, the Greek cities that sat on the sidelines quickly flocked to join the victors.
