These are independent novels chronicling the history of Britain from the time of the Roman legions to the early Briton kingdoms after the withdrawal of the Roman troops. There are some connections between the books - the descendents of some of the characters from the first book appear later on - but the books don't necessarily have to be read in order. The first three books were published in an omnibus entitled "Three Legions". The fourth, "Sword at Sunset", isn't always included in the series, but it continues the story of Artos - the King Arthur of legend - begun in "The Lantern Bearers", and includes some of the same characters.