G. A. Henty 
Beric the Briton – a Story of the Roman Invasion [EPUB ebook] 

The hero of the story is Beric, a young Briton, currently living under Roman subjugation. After he is raised to the rank of chief among his tribe, known as the Iceni, he and his tribe rise up against Roman rule. The strong but untrained Britons are successful in the beginning of the uprising, but are quickly conquered again by the well-trained legionaries. Beric and his small group of men fight to the last, conducting a sort of guerrilla warfare. Finally he and his men are captured, and Beric is sent to Rome as a prisoner/gladiator. In Rome, he becomes friends with some people who belong to the rising sect of Christians. When a Christian girl is about to be given to the lions in the Roman amphitheater, Beric dashes to the rescue and kills a lion single-handedly…