In a huge alluvial plain, often covered by water and crossed by the slow-flowing River Esen Cayi, is Letoon, the religious centre of ancient Xanthos and sanctuary of Leto, now a Unesco site. Three temples (c 2C BC) stand as a reminder of the cult to the goddess Leto and her children, Apollo and Artemis, and fragments of columns, capitals and a mosaic can still be seen here. The Roman nymphaeum has retained its pool and the Hellenistic theatre still boasts a superb frieze of masks.