Don’t bother reading the whole Historia, you can stick to the two Arthurian sections: Merlin’s prophecies and the story of King Arthur. The Historia laid the template for subsequent Arthurian literature by establishing the story from birth to death of Arthur as the greatest king of the Britons, who ultimately fell due to his nephew Mordred’s treachery. In the Historia, Arthur’s story is part of a longer, often dull to the modern eye, chronicle of Britain’s real and legendary kings since Brutus, a fictional Trojan exile, established himself on the island. Accessorily useful as an early formulation of King Lear’s story, better known to us through Shakespeare, who borrowed it from different sources.