The ecumene (U.S. spelling) or oecumene (UK spelling; ) is an ancient Greek term for the known, the inhabited, or the habitable world. In Greek antiquity, it referred to the portions of the world known to Hellenic geographers, subdivided into three continents (Africa, Europe, and Asia). Under the Roman Empire, it came to refer to civilization itself, as well as the secular and religious imperial administration. In present usage, it is most often used in the context of "ecumenical" and describes the Christian Church as a unified whole, or the unified modern world civilization. It is also used in cartography to describe a type of world map (mappa mundi) used in late antiquity and the Middle Ages. Etymology The Greek term cited above is the feminine present middle participle of the verb (, '(I) inhabit') and is a clipped form of (, 'inhabited world'). Greece Ancient Greek and Roman geographers knew the approximate size of the globe, but remained ignorant of many parts of it. Eratosthenes of Cyrene (276–196 BC) deduced the circumference of the Earth with remarkable accuracy (within 10% of the correct value). The Greek cartographer Crates created a globe about 150 BC. Claudius Ptolemy (83–161) calculated the Earth's surface in his Geography and described the inhabited portion as spanning 180 degrees of longitude (from the Fortunate Isles in the west to Serica (northern China) in the east) and about 80 degrees of latitude (from Thule in the north to anti-Meroë below the equator). At its widest possible extent, the ancient ecumene thus stretched from northern Europe to equatorial Africa, and from the Atlantic Ocean to western China. During the Middle Ages, this picture of the world was widened to accommodate Scandinavia, the North Atlantic, East Asia, and eventually sub-equatorial Africa. Ptolemy and other ancient geographers were well aware that they had a limited view of the ecumene, and that their knowledge extended to only a quarter of the globe. These geographers acknowledged the existence of terrae incognitae ('unknown lands') within Africa, Europe and Asia. In fact, a belief in global symmetry led many Greco-Roman geographers to posit other continents elsewhere on the globe, which existed in balance with the ecumene: Perioeci ( 'beside the ecumene'), Antoeci ('opposite the ecumene') and the Antipodes ('opposite the feet'). Rome The cameo Gemma Augustea includes a Roman artistic personification of Oikoumene as she crowns an emperor, probably Augustus, perhaps for bringing