CEOS (Gr. Kiws, mod. Zea or Tzia)  , an island in the Aegean Sea, belonging to the group of the Cyclades and the eparchy of Syra, 14 M. off the coast of Attica . Its greatest length is about 15 M. and its breadth about 8 m . It rises gradually towards the centre, where it culminates in Mount Elias, 1864 ft. high . Among its natural productions are lemons, citrons, olives, wine and honey; it also exports a considerable quantity of valonia . There were formerly four towns of some importance in the island:—Iulis, about 3 M. from the north-west shore; Coressia, the harbour of Iulis, with a temple of Apollo Smintheus in the neighbourhood; Carthaea, in the south-east, with a temple of Apollo; and Poieessa in the south-west . Of these lulls is represented by the town of Zea, and Carthaea by the village of 'S tais Polais; traces of the other two can still be made out . Iulis was the birthplace of the lyric poets Simonides and Bacchylides, the philosophers Prodicus and Ariston, and the physician Erasistratus; the excellence of its laws was so generally recognized that the title of Cean Laws passed into a proverb . One of them forbade a citizen to protract his life beyond sixty years . The people of Ceos fought on the Greek side at Artemisium and Salamis; they joined the Defian League and also the later Athenian alliance in 377 B.C . They revolted in 363-362, but were reduced again, and the Athenians established a monopoly of the ruddle, or red earth, which was one of the most valuable products of the island . In A.D . 1207 it was divided between four Italian adventurers; after forming part of the duchy of Naxos in 1537, it passed under Turkish rule in 1566 .

Silver coins of Carthaea and Coressia have been found dating from the 6th century B.C . (see NUMISMATICS: Greek, " Cyclades and Sporades ") . The present population of the island is about 4000, of which the capital has about 2000 . See Pridik, De Cei Insulae rebus (1892) . (E .