Sebastian is both a given name and a surname. It comes from the Greek name Sebastianos (Σεβαστιανός) meaning "from Sebastia" (Σεβάστεια), which was the name of the city now known as Sivas, located in the central portion of what is now Turkey; in Western Europe the name comes through the Latinized intermediary Sebastianus. It was a name of ancient Greek origin, given to children not born free and found on the streets of Sebastia. The name of the city is derived from the Greek word σεβαστός (sebastos), "venerable", which comes from σέβας (sebas), "awe, reverence, dread", in turn from the verb σέβομαι (sebomai), "feel awe, scruple, be ashamed". Sebastos was the Greek calque of the title Augustus, which was used for Roman emperors. Sebastian became a widely used name because it was the name of Saint Sebastian, a third-century Christian martyr.

Sivas is a city in central Turkey. It is the seat of Sivas Province and Sivas District. Its population is 365,274 (2022).