Cosmas Indicopleustes was a Greek-speaking merchant, traveler, and monk who lived and wrote in the 6th century CE, likely during the reign of Emperor Justinian I. His name means "sailor to India," reflecting his career as a merchant who traded across the Red Sea and Indian Ocean. His travels took him to places including Ethiopia, Sri Lanka, and India. Later in life, he retired from commerce and became a monk, possibly at a monastery on the Sinai Peninsula. He was a devout Christian of the Nestorian tradition, which differed from the official church of the Byzantine Empire.

He is known for a single work, the Christian Topography, a multi-volume treatise that combines cosmology, geography, theology, and his own travel experiences. The work survives in several later illustrated manuscripts. Its significance is twofold. First, it provides valuable firsthand accounts of the 6th-century Indian Ocean trade network, describing the cultures, economies, and geography of regions he visited. Second, and more famously, the work is a passionate argument for a biblical view of the universe against the spherical earth model of classical Greek science. Cosmas argued that the world was flat and that the cosmos was shaped like the Tabernacle described in the Bible. According to modern scholars, while his cosmological ideas were not widely adopted and were even criticized in his own time, his book remains a crucial source for understanding the conflict between Christian and classical worldviews in late antiquity and for the history of early medieval trade and exploration.