Plutarch, Cleomenes
Bernadotte Perrin, Ed.

19. Thus Argos was taken by Cleomenes, and immediately afterwards Cleonae and Phlius came over to him. When this happened, Aratus was at Corinth, holding a judicial examination of those who were reputed to favour the Spartan cause. The unexpected tidings threw him into consternation, and perceiving that the city was leaning towards Cleomenes and wished to be rid of the Achaeans, he summoned the citizens into the council-hall, and then slipped away unnoticed to the city gate. There his horse was brought to him, and mounting it he fled to Sicyon. [2] The Corinthians were so eager to get to Cleomenes at Argos that, as Aratus says, all their horses were ruined. Aratus says also that Cleomenes upbraided the Corinthians for not seizing him, but letting him escape; however, Megistonoüs came to him, he says, bringing from Cleomenes a request for the surrender of Acrocorinthus (which was held by an Achaean garrison) and an offer of a large sum of money for it; to which he replied that he did not control affairs, but rather affairs controlled him. This is what Aratus writes.

[3] But Cleomenes, marching up from Argos and taking over Troezen, Epidaurus, and Hermioné, came to Corinth. Its citadel he blockaded, since the Achaeans would not abandon it, and after summoning the friends and stewards of Aratus, ordered them to take the house and property of Aratus into their charge and management. [4] Then he sent Tritymallus the Messenian once more to Aratus, proposing that Acrocorinthus should be garrisoned by Achaeans and Lacedaemonians together, and promising Aratus personally double the stipend which he was receiving from King Ptolemy.¹ Aratus, however, would not listen to the proposition, but sent his son to Antigonus along with the other hostages, and persuaded the Achaeans to vote the surrender of Acrocorinthus to Antigonus. Therefore Cleomenes invaded the territory of Sicyon and ravaged it, and accepted the property of Aratus when the Corinthians voted it to him as a gift.