Cleomenes' defensive front near the Isthmus of Corinth proved very effective. It took Antigonus a long time to overcome it, and he lost men while trying to break through near Lechaeum. Later, a delegation from Argos asked Aratus to liberate their city from the Spartans, as Cleomenes had failed to deliver on his promises. Aratus sailed to Epidaurus with 1,500 troops to attack Argos, but found that it had fallen already to an internal uprising with the help of Timoxenos, then "strategos" of the Achaean League. Sparta was left almost undefended. Cleomenes was forced to return to Sparta as a result, and leave his defences near the Isthmus. This allowed Antigonus to enter the Peloponnese, where he occupied the Acrocorinth and put a garrison in the city.