Greek historian Arrian of Nicomedia (Latin: Lucius Flavius Arrianus; (c.95- c.180 CE) served in the Roman army and as prefect and legate of Cappadocia (131-37) before retiring to Greece and writing eight historical and philosophical works, four of which have survived. His Anabasis of Alexander has been considered the best source on the campaigns of Alexander the Great, although recent writers have questioned his methodology. See here for a more detailed biographical sketch.