the worst, the Romans began a major mobilization, all but pulling out of recently pacified Spain and Gaul. They even established a major garrison in Sicily in case the Seleucids ever got to Italy. This fear was shared by Rome's Greek allies, who had largely ignored Rome in the years after the Second Macedonian War, but now followed Rome again for the first time since that war. A major Roman-Greek force was mobilized under the command of the great hero of the Second Punic War, Scipio Africanus, and set out for Greece, beginning the Roman–Seleucid War. After initial fighting that revealed serious Seleucid weaknesses, the Seleucids tried to turn the Roman strength against them at the Battle of Thermopylae (as they believed the 300 Spartans had done centuries earlier). Like the Spartans, the Seleucids lost the battle, and were forced to evacuate Greece. The Romans pursued the Seleucids by crossing the Hellespont, which marked the first time a Roman army had ever entered Asia. The decisive engagement was fought at the Battle of Magnesia, resulting in a complete Roman victory. The Seleucids sued for peace, and Rome forced them to give up their recent Greek conquests. Although they still controlled a great deal of territory, this defeat marked the decline of their empire, as they were to begin facing increasingly aggressive subjects in the east (the Parthians) and the west (the Greeks). Their empire disintegrated into a rump over the course of the next century, when it was eclipsed by Pontus. Following Magnesia, Rome again withdrew from Greece, assuming (or hoping) that the lack of a major Greek power would ensure a stable peace. In fact, it did the opposite. Conquest of Greece In 179, Philip died. His talented and ambitious son, Perseus, took the throne and showed a renewed interest in conquering Greece. With her Greek allies facing a major new threat, Rome declared war on Macedonia again, starting the Third Macedonian War. Perseus initially had some success against the Romans. However, Rome responded by sending a stronger army. This second consular army decisively defeated the Macedonians at the Battle of Pydna in 168 and the Macedonians capitulated, ending the war. Convinced now that the Greeks (and therefore the rest of the region) would not have peace if left alone, Rome decided to establish its first permanent foothold in the Greek world, and divided Macedonia into four client republics.