Geryoneo, another tyrant in Book 5, is a big problem—literally. This half-giant figure has wormed his way into the good graces of the widow Belge in order to take control of her kingdom for himself. And if you weren't already clear that this is not a good thing to do, he goes ahead and sacrifices most of her children just to underscore his villainous nature. Eeek.
Belge's name is meant to evoke the country of Belgium, and so Geryoneo's conquest of her land is a representation of the Spanish conquest of the Low Countries that England attempted to prevent. Arthur's defeat of Geryoneo is further representation of English victory over Spain. Geryoneo's establishment of an idolatrous religious presence in addition to his political tyranny underscores a common theme in the poem that bad government is necessarily connected to bad moral systems.