SPARTA, GREECE—Conservators working under the auspices of Greece’s Central Archaeological Council are studying how to rehabilitate the ruins of Sparta’s ancient theater. Built of local white marble during the Roman period, the late first-century B.C theater was one of the Classical world’s largest. Said to be capable of holding an estimated 16,000 people, it featured a mobile stage and was considered a tourist destination in ancient times. Much of the auditorium was destroyed during the Byzantine period, and the remaining marble and limestone blocks have suffered from erosion.