The deaths of Philip's elder brothers, King Alexander II and Perdiccas III, allowed him to take the throne in 359 BC. Originally appointed regent for his infant nephew Amyntas IV, who was the son of Perdiccas III, Philip succeeded in taking the kingdom for himself that same year. Philip's military skills and expansionist vision of Macedonian greatness brought him early success. He first had to remedy a predicament which had been greatly worsened by the defeat against the Illyrians in which King Perdiccas himself had died. The Paionians and the Thracians had sacked and invaded the eastern regions of Macedonia, while the Athenians had landed, at Methoni on the coast, a contingent under a Macedonian pretender called Argeus. Using diplomacy, Philip pushed back the Paionians and Thracians promising tributes, and crushed the 3,000 Athenian hoplites (359). Momentarily free from his opponents, he concentrated on strengthening his internal position and, above all, his army. His most important innovation was doubtless the introduction of the phalanx infantry corps, armed with the famous sarissa, an exceedingly long spear, at the time the most important army corps in Macedonia. Philip had married Audata, great-granddaughter of the Illyrian king of Dardania, Bardyllis. However, this did not prevent him from marching against the Illyrians in 358 and crushing them in a ferocious battle in which some 7,000 Illyrians died (357). By this move, Philip established his authority inland as far as Lake Ohrid and earned the favour of the Epirotes. The Athenians had been unable to conquer Amphipolis, which commanded the gold mines of Mount Pangaion. So Philip reached an agreement with Athens to lease the city to them after its conquest, in exchange for Pydna (lost by Macedon in 363). However, after conquering Amphipolis, Philip kept both cities (357). As Athens had declared war against him, he allied Macedon with the Chalkidian League of Olynthus. He subsequently conquered Potidaea, this time keeping his word and ceding it to the League in 356. In 357 BC, Philip married the Epirote princess Olympias, who was the daughter of the king of the Molossians. Alexander was born in 356, the same year as Philip's racehorse won at the Olympic Games. During 356 BC, Philip conquered the town of Crenides and changed its name to Philippi.