(Περδίκκας), king of Macedonia, was the son and successor of Alexander I. It is impossible to fix the date of his accession with any degree of precision, on account of the great discrepancy in the statements of ancient authors concerning the length of his reign, to which Dexippus and Eusebius allot only twenty-two or twenty-three years, while Theopompus extended it to thirty-five, and the Parian Chronicle, apparently following Nicomedes of Acanthus, to as much as forty-one years. (See Athen. 5.217; Clinton, F. H. vol. ii. p. 222; Dexipp. apud Syncell. p. 262d; Marm. Par.) It is certain, however, that he had been on the throne of Macedonia for some time when his name first appears in history, shortly before the outbreak of the Peloponnesian war. During the early years of his reign he had entertained friendly relations with the Athenians, who, as it appears, had even bestowed on him the rights of a citizen as a reward for the services of his father Alexander during the Persian war. (Thuc. 1.57; Demosth. de Syntax. p. 173, c. Aristocr. p. 687, who erroneously calls Perdiccas king at the time of the Persian invasion.) But the countenance furnished by the Athenians to the pretensions of his brother Philip, as well as to Derdas, a Macedonian chieftain, at this time in hostility to Perdiccas, completely estranged the mind of the latter, and led to an open rupture between him and Athens. In B. C. 432, the Athenians sent a fleet and army to Macedonia to support Philip and Derdas against Perdiccas, while the latter openly espoused the cause of Potidaea, which had shaken off the Athenian yoke, at the same time that he sent ambassadors to Lacedaemon and Corinth, to induce those powerful states to declare war against Athens. His negotiations, for a time, produced no effect. But the Athenian generals also accomplished but little : they took Therma, but laid siege, without effect, to Pydna, and concluded a hasty treaty with Perdiccas, in order to be more at liberty to pursue operations against Potidaea. This peace, however, was broken almost immediately afterwards, and Perdiccas sent a body of horse to the assistance of the Potidaeans, but these troops failed in operating a diversion in favour of their allies. (Thuc. 1.57_59, 61-63; Diod. 12.34.) Perdiccas, however, continued on hostile terms with Athens, until the following year (B. C. 431), when Nymphodorus brought about a peace between them by which the Macedonian king obtained the restoration of Therma. He now supported the Athenian general Phormion against the Chalcidians. but his disposition seems to have been still unfriendly, and we find him soon after sending secret assistance to the expedition of the Ambraciots and their allies against Acarnania. (Id. 2.29, 80.)

He was soon threatened by a more formidable danger. In B. C. 429, Sitalces, king of the powerful Thracian tribe of the Odrysians, invaded Macedonia with an army of 150,000 men, with the declared object of establishing Amyntas, the son of Philip, upon the throne of that country. Perdiccas was wholly unable to oppose this mighty host, and contented himself with observing their movements, harassing them with his light cavalry, and cutting off their supplies. The very magnitude of the barbarian army proved the cause of its failure. Sitalces, indeed, ravaged the open country without opposition, and took some small towns, but was disappointed of the promised co-operation of the Athenian fleet, and after a short stay in Chalcidice, was compelled, by want of provisions, to return home. Seuthes, the nephew of the Thracian king, who had been secretly gained over by Perdiccas, was mainly instrumental in bringing about this resolution, in reward for which service Perdiccas gave him his sister Stratonice in marriage. (Thuc. 2.95_101; Diod. 12.50, 51.)

From this time we hear no more of the proceedings of Perdiccas for some years, but he appears to have continued always on hosthe terms with Athens, and it was in great part at his instigation that Brasidas in B. C. 424 set out on his celebrated expedition to Macedonia and Thrace. (Thuc. 4.79.) Immediately on the arrival of the Spartan general, Perdiccas made use of his new auxiliary to prosecute a private quarrel of his own with Arrhibaeus, prince of Lyncestis. But Brasidas, though he at first joined his forces with those of the Macedonian king, interposed rather as a mediator than an auxiliary, and soon concluded a treaty with Arrhibaeus, by which proceeding he so much offended Perdiccas, that the latter withdrew a part of the supplies which he had engaged to furnish to the Lacedaemonian army, and took little part in the operations of Brasidas in Chalcidice and Thrace. But the following spring (B. C. 423) the conclusion of a truce for a year between the Athenians and Lacedaemonians having suspended the operations of Brasidas, Perdiccas induced him once more to join in a campaign against Arrhibaeus. The king had also reckoned on the cooperation of a body of Illyrians, but these expected allies suddenly joined the enemy, and the Macedonian troops, alarmed at their defection, were seized with a panic, and compelled Perdiccas to make a hasty retreat, leaving his Spartan auxiliaries at the mercy of the enemy. Brasidas, indeed, saved his army by a masterly retreat, but the minds of the Spartans were irritated against the Macedonian king, and it was not long before matters came to an open rupture. Before the close of the year Perdiccas abandoned the Spartan alliance, and concluded peace with Athens. (Thuc. 4.82, 83, 103, 107, 124-128, 132.)

But he was little disposed to enter heartily into the cause of his new allies, whom he supported so feebly as to lead to the failure of their arms in Chalcidice, and in B. C. 418 he secretly joined the new league concluded between Sparta and Argos. This led to a renewal of hostilities between him and the Athenians, but apparently without any important result. At a subsequent period we find him again in alliance with Athens, without any account of the circumstances that led to this change; but it is evident that he joined one or other of the belligerent parties according to the dictates of his own interest at the moment. (Thuc. 5.80, 83. 6.7, 7.9.) The exact date of the death of Perdiccas cannot be determined, but it is clear from Thucydides that it could not have occurred before the end of B. C. 414, or the beginning of 413. The Parian Chronicle, by a strange error, assigns it to the archonship of Astyphilus, B. C. 420. (Thuc. 7.9; Marm. Par.; Clinton, F. H. vol. ii. pp. 74, 223.)