The Stronghold protects your units from enemy attacks (e.g. they will not be wounded by an attack). When you put units in the keep they will not be stationed on the wall, but will participate in the courtyard battle. Each level will have capacity for more units.
|Level||Rubies cost||Units protected|
|1||175 wood & 130 stone||20|
|2||3,011 wood & 4,218 stone||50|