Eros (, ; ) is a concept in ancient Greek philosophy referring to sensual or passionate love, from which the term erotic is derived. Eros has also been used in philosophy and psychology in a much wider sense, almost as an equivalent to "life energy". The Protestant author C. S. Lewis posits it as one of the four ancient Greek words for love in Christianity, alongside storge, philia, and agape. In literature The classical Greek tradition In the classical world, erotic love was generally referred to as a kind of madness or theia mania ("madness from the gods"). This love passion was described through an elaborate metaphoric and mythological schema involving "love's arrows" or "love darts", the source of which was often the personified figure of Eros (or his Latin counterpart, Cupid), or another deity (such as Rumor). At times the source of the arrows was said to be the image of the beautiful love object itself. If these arrows were to arrive at the lover's eyes, they would then travel to and 'pierce' or 'wound' their heart and overwhelm them with desire and longing (lovesickness). The image of the "arrow's wound" was sometimes used to create oxymorons and rhetorical antithesis concerning its pleasure and pain. "Love at first sight" was explained as a sudden and immediate beguiling of the lover through the action of these processes, but this was not the only mode of entering into passionate love in classical texts. At times the passion could occur after the initial meeting; for example, in Phaedra's letter to Hippolytus in Ovid's Heroides: "That time I went to Eleusis... it was then most of all (though you had pleased me before) that piercing love lodged in my deepest bones." At times, the passion could even precede the first glimpse, as in Paris' letter to Helen of Troy in the same work, where Paris says that his love for Helen came upon him before he had set eyes on her: "...you were my heart's desire before you were known to me. I beheld your features with my soul ere I saw them with my eyes; rumour, that told me of you, was the first to deal my wound." Whether by "first sight" or by other routes, passionate love often had disastrous results according to the classical authors. In the event that the loved one was cruel or uninterested, this desire was shown