COSMAS, of Alexandria, surnamed from his maritime ex perience Indicopleustes, merchant and traveller, flourished dur ing the 6th century A.D. In his earlier days he had sailed on the Red sea and the Indian ocean, visiting Abyssinia and Socotra and apparently also the Persian gulf, western India and Ceylon. He subsequently became a monk, and about 548, in the retire ment of a Sinai cloister, wrote a work called Topographia Chris tiana. Its chief object is to denounce the false and heathen doctrine of the rotundity of the earth, and to vindicate the scrip tural account of the world. According to Cosmas the earth is a rectangular plane, covered by the vaulted roof of the firmament, above which lies heaven. In the centre of the plane is the in habited earth, surrounded by ocean, beyond which lies the para dise of Adam. The sun revolves round a conical mountain to the north—round the summit in summer, round the base in winter, which accounts for the difference in the length of the day. Cosmas is supposed by some to have been a Nestorian. The Topographia contains some curious information. Especially to be noticed is the description of a marble seat discovered by him at Adulis (Zula) in Abyssinia, with two inscriptions recounting the heroic deeds and military successes of Ptolemy Euergetes and an Axu mitic king. It also contains in all probability the oldest Christian maps. From allusions in the Topographia Cosmas seems to have been the author of a larger cosmography, a treatise on the motions of the stars, and commentaries on the Psalms and Canticles.