2. Succeeded Aristippus II. in the tyranny of Argos, apparently towards the end of the reign of Demetrius. (B. C. 240-230.) He seems to have been related to some of his predecessors in the tyranny of Argos. (Plb. 2.59.) After the death of Demetrius, B. C. 229, he resigned his power, as Lydiades had done before, and several others did now, for the influence of Macedonia in Peloponnesus had nearly ceased, and the Aetolians were allied with the Achaeans. Aristomachus had been persuaded to this step by Aratus, who gave him fifty talents that he might be able to pay off and dismiss his mercenaries. Argos now joined the Achaean league, and Aristomachus was chosen strategus of the Achaeans for the year B. C. 227. (Plut. Arat. 35; Plb. 2.44; Paus. 2.8.5 ; Plut. Cleom. 4.) In this capacity he undertook the command in the war against Cleomenes of Sparta, but he seems to have been checked by the jealousy of Aratus, in consequence of which he afterwards deserted the cause of the Achaeans and went over to Cleomenes, who with his assistance took possession of Argos. Aristomachus now again assumed the tyranny at Argos. Aratus tried in vain to recover that city for the Achaean league, and the consequence only was, that the tyrant ordered 80 distinguished Argives to be put to death, as they were suspected of being favourable towards the Achaeans. Not long afterwards, however, Argos was taken by Antigonus Doson, whose assistance Aratus had called in. Aristomachus fell into the hands of the Achaeans, who strangled him and threw him into the sea at Cenchreae. (Plb. 2.59, 60; Plut. Arat. 44; Schorn, Geschichte Griechenl. p. 118, note 1.)