Cosmas in Harpers Dictionary of Classical Antiquities (1898)
（Κοσμᾶς). An Egyptian priest, often called Indopleustes (Ἰνδοπλευστής) from his voyages, who lived about A.D. 535. In his youth he was engaged in foreign trade and visited many countries, of which he wrote an account in twelve books, most of which are extant. The work was styled Τοπογραφία Χριστιανεκή. In it China is first undeniably mentioned, being styled Tzinista-the Persian Chinistan. Edition by Gallandi (1776).
Cosmas Indicopleustes in Wikipedia
Cosmas Indicopleustes (literally "who sailed to India") of Alexandria was a Greek merchant and later monk probably of Nestorian tendencies. He was a 6th century traveller, who made several voyages to India during the reign of emperor Justinian. His Topografia Christiana (Christian Topography) contained some of the earliest and most famous world maps.
Around 550 Cosmas wrote the once-copiously illustrated Christian Topography, a work partly based on his personal experiences as a merchant on the Red Sea and Indian Ocean in the early 6th century. His description of India and Sri Lanka during the 6th century is invaluable to historians. Cosmas seems to have personally visited the Kingdom of Axum in modern Ethiopia, as well as Eritrea, India, and Sri Lanka.
"Indicopleustes" means "Indian voyager". While it is known from classical literature, especially the Periplus Maris Erythraei that there had been trade between the Roman Empire and India from the first century BCE onwards, Cosmas's report is one of the few from individuals who had actually made the journey. He described and sketched some of what he saw in his Topography. Some of these have been copied into the existing manuscripts, the oldest dating to the ninth century. In 522 CE, he visited the Malabar Coast (South India). He is the first traveller to mention about Syrian Christians in India. He wrote, "In the Island of Taprobane (Ceylon), there is a church of the Christians, and clerks and faithful. Likewise at Malé where the pepper grows; and in the town of Kalliana there is also a bishop consecrated in Persia." (Reference: Travancore Manual, page 248).
A major feature of his Topographia is Cosmas' worldview that the world is flat, and that the heavens form the shape of a box with a curved lid. He was scornfull of Ptolemy and others who held that the world was spherical. Cosmas aimed to prove that pre-Christian geographers had been wrong in asserting that the earth was spherical and that it was in fact modelled on the tabernacle, the house of worship described to Moses by God during the Jewish Exodus from Egypt. However, his idea that the earth is flat has been a small minority view in educated Western opinion since the third century BCE. Cosmas's view has never been influential even in religious circles; a near-contemporary Christian, John Philoponus, disagreed with him as did most Christian philosophers of the era.
Cosmology aside, Cosmas proves to be an interesting and reliable guide, providing a window into a world that has since disappeared. He happened to be in Adulis on the Red Sea Coast of modern Eritrea at the time (ca. 525 CE) when the King of Axum was preparing a military expedition to attack the Jewish king Dhu Nuwas in Yemen, who had recently been persecuting Christians. On request of the Axumite king and in preparation for this campaign he recorded now-vanished inscriptions such as the Monumentum Adulitanum (which he mistakenly attributed to Ptolemy III Euergetes).