The Thessalian League originated in the deliberate choice by village aristocracies of a single monarch who belonged from time to time to several of the so-called Heracleid families.
In accordance with the tradition which assigned the portion to the eldest-born of the Heracleid conquerors, Argos was for some centuries the leading power in Peloponnesus.
The last of these attempts resulted in the " Dorian conquest " of the "Achaeans " and " Ionians " of Peloponnese, and in the assignment of Argolis, Laconia and Messenia to the Heracleid leaders, Temenus, Aristodemus and Cresphontes respectively; of Elis to their Aetolian allies; and of the north coast to the remnants of the conquered Achaeans.
The conquest of Laconia at least is represented in 5th-century tradition as immediate and complete, though one legend admits the previous death of the Heracleid leader Aristodemus, and another describes a protracted struggle in the case of Corinth.
The 5th-century tradition that the Heracleid kings of Macedon were Temenid exiles from Argos may belong to the same cycle.