Emperor — Stephen Baxter

It is the Prophecy. Inscribed in Latin, the ancient scroll has resided in the hands of a single family for generations, revealing secrets about the world, that is to come and guiding them to wealth and power. It begins when a Celtic noble betrays his people at the behest of his mother's belief in the Prophecy -- and sides with the conquering Roman legions.

For the next four hundred years, Britannia thrives, as does the family, while Rome rules over the island. But loyalties are torn when Constantine, the most powerful Emperor of them all, comes to Britannia.

And even as the sun begins to set on the Roman Empire, the Prophecy is renewed -- a message from an unknowable future, promising the world to those who can decipher its cryptic words...