THAIS, a Greek courtesan, who lived during the time of Alexander the Great. She accompanied him on his Asiatic campaign, and is chiefly known from the story which represents her as having persuaded the conqueror to set fire to the city of Persepolis. This anecdote forms the subject of Dryden's Ode to Saint Cecilia's Day. But its authenticity is doubtful, since it is based upon the authority of Cleitarchus, one of the least trustworthy of the historians of Alexander. Thais subsequently became the wife of Ptolemy Lagus, king of Egypt. Numerous anecdotes and witticisms attributed to her will be found in Athenaeus. See Diod. Sic. xvii. 72; Plutarch, Alexander, 38; Athenaeus xiii. 576, 585; Quintus Curtiusv. 7.