3. But the expulsion of the Persians still left Macedonia exposed to the attacks of other formidable neighbours; on one side there was the Thracians, among whom, under Sitalces, and his successor, Seuthes, arose the powerful kingdom of the Odrysae; on the other, the Athenians, who, availing themselves of their extensive navy, reduced to subjection the Grecian settlements on the Macedonian shores. Harassing as these neighbours were to the Macedonian kings, they proved to be the very instruments by which Macedonia became so early and so deeply involved in the affairs of Greece. Commencement of the differences with Athens, under the reign of Perdiccas II, 454-413; Athens having supported his brother Philip against him.--Defection of Potidaea, and fortification of Olynthus, into which the Greeks from Chalcis and other cities are transplanted, 432. Potidaea being forced to surrender to Athens, 431, Perdiccas contrives to play so skilful a part in the Peloponnesian war just now commencing, that he outwits the Athenians, parrying the attack of Sitalces by a marriage of his sister with Seuthes, the heir to that prince, 429. His alliance with Sparta, 424, is very detrimental to the Athenians, Brasidas wresting Amphipolis from their hands; nevertheless Perdiccas chooses rather to conclude a peace with Athens, 423, than to throw himself entirely into the arms of his new allies. 4. Archelaus, the successor of Perdiccas, introduced agriculture and civilization among the Macedonians, who were never, however, recognized by the Hellenes as their legitimate brethren: highways and military roads were constructed; forts were erected; and the court became the seat of literature. In these days the Macedonian kingdom seems to have comprised Emathia, Mygdonia, and Pelagonia, to which may be added some of the neighbouring tribes, who, although governed by their own kings, were tributary. The power of the kings was insignificant when unaided by the nobles, among whom, as was the case with all the hereditary princes of Greece, they merely held the right of precedence. How difficult was it, even in Alexander's time, to erase from the minds of the Macedonian nobility the recollection of their former importance! 5. The murder of Archelaus was followed by a stormy period, wrapped in obscurity: the unsettled state of the succession raised up many pretenders to the throne, each of whom easily found the means of supporting his claims, either in some of the neighbouring tribes, or in one of the Grecian republics.