This place was once the outpost of the Temple of Elemental Evil, its watchtower an advance base of raids, looting, and destruction. From this area, servants of the Temple were to bring the Village of Hommlet and all the lands around it into subjection. The conquered folk were then to be used as slaves to construct yet another fortress further west, spreading the evil power of the Temple in ever-growing rings to encompass all of the lands around its base.
This outpost was ignored during the destruction of the Temple, for the army of good which came against the wicked hordes was so strong to be totally immune to any pinpricking from the garrison of the moathouse. Only after the end of the battle which destroyed the main armies of the Temple of Elemental Evil was attention turned to this place.
... the moathouse was surrounded, cut-off, and battered into extinction.