A Ring-city was a type of city that could be found on the planet of Kaikielius.
History
In 4225 BBY, the Hutt Odominic kajidic began supplying black market arms to Kaikielius, resulting in a war in the planet's ring-cities, between criminals and the police. The Galactic Republic sent troops to Kaikielius to intervene and they attacked the most criminal-infested ring-cities.
Sources
Tinker, Tailor, Soldier, Praji on Hyperspace (article) (content obsolete and backup link not available) (First mentioned)