In 341 BC Demosthenes was sent to Byzantium, where he sought to renew its alliance with Athens. Thanks to Demosthenes' diplomatic manoeuvres, Abydos also entered into an alliance with Athens. These developments worried Philip and increased his anger at Demosthenes. The Assembly, however, laid aside Philip's grievances against Demosthenes' conduct and denounced the peace treaty; so doing, in effect, amounted to an official declaration of war. In 339 BC Philip made his last and most effective bid to conquer southern Greece, assisted by Aeschines' stance in the Amphictyonic Council. During a meeting of the Council, Philip accused the Amfissian Locrians of intruding on consecrated ground. The presiding officer of the Council, a Thessalian named Cottyphus, proposed the convocation of an Amphictyonic Congress to inflict a harsh punishment upon the Locrians. Aeschines agreed with this proposition and maintained that the Athenians should participate in the Congress. * C. Carey, "Aeschines", 7–8.</ref> Demosthenes however reversed Aeschines' initiatives and Athens finally abstained. After the failure of a first military excursion against the Locrians, the summer session of the Amphictyonic Council gave command of the league's forces to Philip and asked him to lead a second excursion. Philip decided to act at once; in the winter of 339–338 BC, he passed through Thermopylae, entered Amfissa and defeated the Locrians. After this significant victory, Philip swiftly entered Phocis in 338 BC. He then turned south-east down the Cephissus valley, seized Elateia, and restored the fortifications of the city.* K. Tsatsos, "Demosthenes", 283; H. Weil, "Biography of Demosthenes", 41–42.</ref>