Troyius was an inhabited planet. This was the homeworld of the Troyians, a spaceflight humanoid species. The planet was farther from its primary than its sister planet Elas. It was located in the Tellun planetary system. This system was located in the Federation-Klingon border.
The planet had rich deposits of dilithium ("radan", Troyian language). In 2268, both planets possessed the capability of mutual destruction. The wedding of the Dohlman of Elas, Elaan, to the ruler of Troyius preserved the peace. (TOS: "Elaan of Troyius")