For nearly half a century Rome and the Achaean League had been allies. The relationship soured as Roman power grew, until the Greeks found themselves treated less like partners than like subjects, and resented it. The break came over Sparta, which the League wanted to absorb and Rome insisted on protecting. Rome sent embassies to the Achaean capital at Corinth; the first arrived with demands so harsh that its envoys were nearly mobbed in the streets, the second more conciliatory but no more successful. Diplomacy failed somewhere in that exchange. Historians still debate whether the Achaean leaders deliberately picked a fight with the greatest power in the Mediterranean, or simply misjudged how far Roman patience would stretch. Either way, the Senate voted for war.

The war was supposed to belong to the consul Lucius Mummius, but he was still in Italy preparing to sail. In the meantime the Senate let a closer commander act: the praetor Quintus Caecilius Metellus Macedonicus, fresh from victory in the Fourth Macedonian War and already stationed with an army in Macedonia. While Critolaos, the League's elected strategos, was busy besieging the rebel town of Heraclea in Trachis, entirely unaware that Rome had declared war, Metellus put his legions on the road south. Speed was the whole campaign. The first the Greeks knew of the threat was the news that a Roman army was nearly upon them.

Metellus' advance caught Critolaos completely off guard. The strategos abandoned the siege and hurried his men toward Scarphe, hoping to reach safety, but the Romans overtook him in the broken country near the gulf. The ancient sources do not describe a proper set-piece battle, the kind where lines form and clash. They describe a wild, panicked rout: the rigid Greek phalanx coming apart on uneven ground, soldiers running, falling, being cut down or seized as prisoners. Estimates place the Achaean dead and captured at well over ten thousand. Critolaos himself vanished. No one could say with certainty whether he was killed, drowned in the marshes near the coast, or took his own life. He simply disappeared, leaving only rumor behind.

The collapse did not end cleanly with the dead on the field. A nineteenth-century historian, drawing on the ancient accounts, described the aftermath in stark terms: some of the defeated Greeks killed themselves, others fled their homes without knowing where they were going, and some turned on their own neighbors, seizing fellow Greeks and handing them to the Romans, or denouncing them as informers. It is the ugliest part of the story and the most human. A society that had gambled on war and lost was now coming apart from the inside, ordinary people scrambling to survive a catastrophe their leaders had walked them into. The grand politics of leagues and senates had become, very suddenly, a matter of who would betray whom.

With the League's main army destroyed almost before the war began, the rest was swift and merciless. Metellus pushed through Boeotia. The Achaeans, refusing peace even now, threw together one last force at Corinth, and there the consul Mummius, arrived at last, defeated it. Then he sacked Corinth itself, one of the great cities of the Greek world, looting its art and selling its people into slavery. The Achaean League was dissolved and all of mainland Greece brought under permanent Roman control. The same year, far to the west, Rome destroyed Carthage. 146 BC closed two ancient worlds at once, and the rout near the Malian Gulf had opened the gate.