Strabo Geography 8.5.4

[4] According to Ephorus: Eurysthenes and Procles, the Heracleidae, took possession of Laconia, ¹ divided the country into six parts, and founded cities; ² now one of the divisions, Amyclae, they selected and gave to the man ³ who had betrayed Laconia to them and who had persuaded the ruler who was in possession of it to accept their terms and emigrate with the Achaeans to Ionia; Sparta they designated as a royal residence for themselves; to the other divisions they sent kings, and because of the sparsity of the population gave them permission to receive as fellow inhabitants any strangers who wished the privilege; and they used Las as a naval station because of its good harbor, and Aegys ⁴ as a base of operations against their enemies (for its territory ⁵ bordered on those of the surrounding peoples) and Pharis as a treasury, because it afforded security against outsiders; . . . but though the neighboring peoples, one and all, were subject to the Spartiatae, still they had equal rights, sharing both in the rights of citizenship and in the offices of state, and they were called Helots; ⁶ but Agis, the son of Eurysthenes, deprived them of the equality of rights and ordered them to pay tribute to Sparta; now all obeyed except the Heleians, the occupants of Helus, who, because they revolted, were forcibly reduced in a war, and were condemned to slavery, with the express reservation that no slaveholder should be permitted either to set them free or to sell them outside the borders of the country; and this war was called the War against the Helots. One may almost say that it was Agis and his associates who introduced the whole system of Helot-slavery that persisted until the supremacy of the Romans; for the Lacedaemonians held the Helots as state slaves in a way, having assigned to them certain settlements to live in and special services to perform.