Who is Caius Porteus from Sarum: The Novel of England and what is their importance?

Caius Porteus was a Roman soldier who was sent to Britannica in 60 AD. After criticizing his superior, Caius is banished to Sorviodunum. He later marries the daughter of the chief Tosutigus and builds himself a Roman style villa. He and his wife, Maeve, have three children.