Plutarch, Cleomenes
Bernadotte Perrin, Ed.

5. After this, he went to the aid of the Eleians, upon whom the Achaeans were making war, and falling upon the Achaeans near Mt. Lycaeum, as they were withdrawing, he put their entire army to panic flight, slew great numbers of them, and took many prisoners, so that even Aratus was widely reported among the Greeks to be dead. But Aratus, making the best use of his opportunity, immediately after this defeat marched to Mantineia, and to everybody's surprise captured and held the city. [2] At this the Lacedaemonians were altogether disheartened and opposed any further expedition on the part of Cleomenes. He therefore determined to summon from Messene the brother of Agis, Archidamus,¹ who was the rightful king from the other royal house, thinking that the power of the ephors would be diminished if the royal power were restored to its full strength so as to counterbalance it. [3] But those who had formerly murdered Agis comprehended this design, and fearing that they would pay the penalty for their crime if Archidamus was restored, they did indeed receive him when he came secretly into the city, and assisted in his restoration, but immediately put him to death. Cleomenes may have been opposed to this, as Phylarchus thinks, or perhaps he was persuaded by his friends to abandon the hapless man to his murderers. For the greater part of the blame attached itself to them, since they were thought to have constrained Cleomenes.