Chains of Promathia, commonly referred to as CoP by English players, is the first expansion to come out after Final Fantasy XI was released outside of Japan. It was designed to be a challenge for hardcore players while also focusing on the delivery of an immersive story with an ensemble cast. For this reason, Chains of Promathia had the longest storyline and some of the hardest missions found in Final Fantasy XI at its release. The difficulty of these missions have since been lowered after years of feedback from players. Service for Chains of Promathia commenced on September 22, 2004 (JST).