Ninth Legion

In the 2nd century, the Roman Ninth Legion invaded Aberdeen, Scotland. The Gatekeeper at the time, Kar, allowed a single Eater of Light to pass through the portal; she thought it would destroy the legion, and become so weakened in the process that it would be easy to defeat. Instead, the creature became stronger after feeding on the Romans and began to darken the sky, threatening the world.

The Twelfth Doctor, along with his companions Bill Potts and Nardole, worked with the Picts and the few surviving Romans to drive the Eater of Light back into the portal. Kar, along with several Picts and the Romans, then entered the portal to fight off the creatures. (TV: The Eaters of Light)