Named after the Town on Santorini Island in the Aegean Sea.
Thira is a crater on Mars. Thira is about 20 km east of the landing site of NASA's Spirit rover. The rim of the crater can be seen in the distance in images taken by Spirit. (wikipedia entry)
A crater is a circular depression likely created by an impact event. On Mars large craters are named after deceased scientists, writers and others who have contributed to the lore of Mars. Small creaters (less than 60km) are named after small towns and villages.