In Episode 3 of the anime series, the Searchers come across the ruins of an English-looking fortress, complete with courtyard and stone archways. The courtyard is full of lost discs (referred to in the anime series as the Grave of the Disc), and they find a Golem guarding the place. He was sworn as its protector by the king from not too long ago, after a battle took place there against Moo's forces.
It is probable that the battle that Holly tells Genki about in Episode 1 of the series (in which a human king tried to fight back against Moo's takeover) took place at this fortress. It is unknown who the king was, since he obviously didn't survive.
The fortress now rests somewhere in the Morx Forest, and it is believed to be the adventure location in My Monster Rancher known as the Phut Graveyard.