Agis and Cleomenes
Plutarch
Plutarch. Plutarch's Lives, Vol. X. Perrin, Bernadotte, translator. Cambridge, MA: Harvard University Press; London: William Heinemann Ltd., 1921.
And yet, desiring to give the name of absolute power a less offensive sound, he associated with himself in royal power his brother Eucleidas. And this was the only time when the Spartans had two kings from the same house.
Learning that Aratus and the Achaeans believed that this revolution had jeopardized his position, and therefore did not think that he would venture forth outside of Sparta, or leave the city while it was still in the suspense of so great an agitation, he thought it a fine and helpful thing to make a display of the ready zeal of his army to his enemies.