A planet of the Tellun star system whose ruler is to marry Elaan of Elas to end the war between their worlds.
Troyius is the outer of the two inhabited planets of the Tellun system, home to the Troyians. The Troyians are more refined than their Elasian rivals, and the two worlds have been at war for a long time.
In Elaan of Troyius, the Enterprise is assigned to carry the Elasian Dohlman Elaan to Troyius for an arranged marriage meant to end the conflict. The Tellun system is close to Klingon space, and its value is increased by the dilithium crystals that both worlds possess.