The Hall of Binding, situated at (J-6) in the Commoner's Ward of Al Zahbi, is the location of the Astral Plinth, where the Astral Candescence is held. Under normal circumstances it is impossible to enter.
During Besieged, the beastmen armies will attack Al Zahbi in an attempt to breach the Hall of Binding and steal the Astral Candescence. Each of the five Serpent Generals has one of the keys necessary to enter the Hall of Binding; this is why it is imperative to defend them, at all costs (it's important to keep in mind though, if they do manage to kill all the generals it's not over yet! Keep fighting and protect the Astral Candescence at all cost!).
If the beastmen manage to take the Astral Candescence, it will be possible to freely enter the Hall of Binding and look upon the Astral Plinth.