Philip's views were first turned towards the eastern frontiers of his dominions, where his interests clashed with those of the Athenians. A few years before the Athenians had made various unavailing attempts to obtain possession of Amphipolis, once the jewel of their empire, but which they had never recovered since its capture by Brasidas in the eighth year of the Peloponnesian war. Its situation at the mouth of the Strymon rendered it also valuable to Macedonia, not only as a commercial port, but as opening a passage into Thrace. The Olynthians were likewise anxious to enrol Amphipolis as a member of their confederacy, and accordingly proposed to the Athenians to form an alliance for the purpose of defending Amphipolis against their mutual enemy. An alliance between these two powerful states would have proved an insurmountable obstacle to Philip's views: and it was therefore absolutely necessary to prevent this coalition. Here we have the first instance of Philip's skill and duplicity in negotiation. By secretly promising the Athenians that he would put Amphipolis into their hands if they would give him possession of Pydna, he induced them to reject the overtures of the Olynthians; and by ceding to the latter the town of Anthemus, he bought off their opposition. He now laid siege to Amphipolis, which, being thus left unaided, fell into his hands (B.C. 358). He then forthwith marched against Pydna, which surrendered to him; but on the ground that it was not the Athenians who had put him in possession of this town, he refused to give up Amphipolis to them. Philip had now just reason to dread the enmity of the Athenians, and accordingly it was his policy to court the favour of the Olynthians, and to prevent them from renewing their negotiations with the Athenians. In order to separate them more effectually, he assisted the Olynthians in recovering Potidaea, which had formerly belonged to their confederacy, but was now in the hands of the Athenians. On the capture of the town he handed it over to the Olynthians. Plutarch relates that the capture of Potidaea was accompanied with three other fortunate events in the life of Philip, namely, the prize gained by his chariot at the Olympic games, a victory of his general Parmenio over the Illyrians, and the birth of his son Alexander. These events happened in B.C. 356. Philip now crossed the Strymon, on the left bank of which lay Pangaeus, a range of mountains abounding in gold-mines. He conquered the district, and founded there a new town called Philippi, on the site of the ancient Thracian town of Crenides. By improved methods of working the mines he made them yield an annual revenue of 1000 talents, nearly 250,000l.