At the western-most edge of their empire, the Romans built a fort, but then they abandoned Britain. Two centuries later, a Christian missionary found reminders of civilisation in the decaying ruin and set up his church there - which still survives, surrounded by Roman walls ten feet high.
But there was more to St Cybi than just a taste for Roman walls. He is known as Cybi Du or Cybi the Black, while his co-religionist at the other end of the island of Anglesey was Seiriol Gwyn, Seiriol the White. Were they just precursors of Tolkein's wizards in "Lord of the Rings", or was there a solid, down-to-earth reason for their colourings?
It's taken four years to get round to fulfilling the promise made in the film about St Seiriol, but here it is at last.