The Greco-Egyptian scientist Claudius Ptolemy referred to the larger island as great Britain (μεγάλης Βρεττανίας - megális Brettanias) and to Ireland as little Britain (μικρής Βρεττανίας - mikris Brettanias) in his work Almagest (147–148 AD). In his later work, Geography (c. 150 AD), he gave these islands the names Alwion, Iwernia, and Mona (the Isle of Man), suggesting these may have been names of the individual islands not known to him at the time of writing Almagest. The name Albion appears to have fallen out of use sometime after the Roman conquest of Great Britain, after which Britain became the more commonplace name for the island called Great Britain.