In his second term, Aratus focused on capturing the Acrocorinth, the acropolis of Corinth. The city of Corinth controlled entry to the Peloponnese, and was an important trading post. The Acrocorinth was a formidable fortress, built on a hill nearly high. It had a freshwater source, was surrounded by cliffs, and was capped by a massive, walled citadel. Antigonus Gonatas controlled the Acrocorinth with a strong garrison under his commander Persaeus. In 243 BC, Aratus learned from Syrian mercenaries that there was a less steep access route to the hill, where the wall was also at its lowest point. By midsummer that year, Aratus was ready to attack the Acrocorinth.