The siege of Trebizond from 1205 to 1206 was an attempt by the Seljuk Sultanate of Rûm to take the city along the coast of the Black Sea.
"[1] Michel Kuršanskis explains that this unsuccessful siege was in response to the Trapezuntine ally, Queen Tamar of Georgia, who had attempted to capture Erzurum in 1205 but failed.
When Sultan Kaykhusraw began his punitive campaign against Trebizond, he found his route limited to a few passes in the Pontic Alps, where the locals harassed his forces.
According to Ali ibn al-Athir, merchants from throughout the Middle East suffered a severe injury because of his siege of Trebizond.
[2] Kuršanskis argues the failure of this siege led to the later successful capture of Sinope in 1214, which provided the Seljuk Turks with an outlet to the Black Sea.