Arcadia

Arcadia was a Human colony world during the Human-Covenant War. It was an Earth-like planet with lots of snow, and was said to be a jewel of the Galaxy. The planet was so beautiful that the Time Lords named one of the cities on Gallifrey after the planet.

The Covenant attacked Arcadia during the Battle of Arcadia and glassed the Human cities there, but they did not glass the entire planet for fear of evoking the wrath of many other races. Their conflict with the Humans had already caused tension between most other races of the League and the Covenant, and they didn't want to push their luck.

Arcadia was also one of the last places that the Spirit of Fire was seen before it was sent hurtling to the other side of the Galaxy, Voyager-style.