In 225 BC, Cleomenes attacked Achaean territory again, aiming to take Aratus' home city, Sicyon. He hoped this would provoke the collapse of the entire Achaean League, as tensions within the League were already running high over Aratus' Macedonian strategy. If Sicyon fell, Aratus would no longer be part of the Achaean League. The plan to take Sicyon failed, but Cleomenes did conquer Pellene, Pheneus, Penteleum, and later Agros. The Argives, never the most enthusiastic members of the Achaean League, decided to ally with Sparta. Many authors see in this the hand of Aristomachus, former tyrant of the city. Aratus was given plenipotentiary powers to deal with the crisis. He marched to Corinth, arriving to face an angry mob: the population had heard of his intention to surrender the city and its citadel to Antigonus. Aratus only narrowly escaped. The Corinthians offered to surrender the city to Cleomenes, even while the Acrocorinth was still held by an Achaean garrison. Cleomenes marched towards Corinth, taking many other cities in Argolis on his way. After laying siege to the Acrocorinth, Cleomenes proposed a peace treaty to Aratus, who refused. The Spartan king went on to besiege Sicyon, pillaging the surrounding countryside.