Cleomenean War in the context of "Critolaos of Megalopolis"

The Achaean League (Ancient Greek: Κοινὸν τῶν Ἀχαιῶν, romanized: Koinon ton Akhaion, lit. 'League of Achaeans') was a Hellenistic-era confederation of Greek city-states on the northern and central Peloponnese. The league was named after the region of Achaea in the northwestern Peloponnese, which formed its original core. The first league was formed in the fifth century BC. Although the first Achaean League is much less well documented than its later revival, it maintained a recognizable federal structure through the early Hellenistic period, but later fell into a period of dormancy under growing Macedonian influence. The more famous second Achaean League was established in 280 BC. First it was an ally of Antigonid Macedon at the Cleomenean War, Social War and First Macedonian War and a rival of the Aetolian League and Sparta. As a rival of Antigonid Macedon and an ally of the Roman Republic since the Second Macedonian War, the league played a major role in the expansion of Rome into Greece. This process eventually led to the League's conquest and dissolution by the Romans in 146 BC.

The League represents the most successful attempt by the Greek city-states to develop a form of federalism, which balanced the need for collective action with the desire for local autonomy. Through the writings of the Achaean historian and statesman Polybius, this structure has had an influence on the constitution of the United States and other modern federal states.

Aratus of Sicyon (Ancient Greek: Ἄρατος ὁ Σικυώνιος; 271–213 BC) was a politician and military commander of Hellenistic Greece. He was elected strategos of the Achaean League 17 times, leading the League through numerous military campaigns including the Cleomenean War and the Social War.

Aratus was exiled to Argos at the age of seven, after his father, the magistrate of Sicyon, was killed in a coup. In 251 BC, he led an expedition composed of other exiles which freed Sicyon from tyranny, and assumed power in the city. Sicyon joined the Achaean League, in which Aratus would later be elected strategos. In his first major campaign as strategos, he seized the Macedonian-held citadel of Acrocorinth, previously believed impregnable.

The Battle of Mount Lycaeum was fought between Sparta led by Cleomenes III and the Achaean League commanded by Aratus. It was the first major battle of the Cleomenean War. The battle occurred at Mount Lycaeum on the border of Elis and Arcadia and ended in a Spartan victory.