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The Castle Siege event takes place in the Valley of Loren. The castle may be ruled by a guild, and if any guild wants, they can lay siege to the castle in an attempt to win possession of it. However, the siege isn’t easy, as the castle is protected by the “home guild” characters and soldiers. This is the "Epic of Loren" quest (the Castle Siege). This is considered to be one of the most amazing parts of MU, and excites all of its users.

The lord of the castle can rule the castle when event starts. He can buy additional troops (archer or spearman) which are NPC's and fight the enemy automatically. The attacking guild also has a few tricks up its sleeve. They can bring special potions for faster attacking and more damage. However the main quest in this event is to defend the castle by defeating the enemy and to not let the attacking guild to destroy the statues of castle. When the statues are destroyed, the attacking guild can easily take the castle and the defenders will lose.