Alphonso de Spina (unknown date of birth – in or about 1491) was a Spanish Franciscan Catholic Bishop, preacher and writer. Thought by many to be a convert from Judaism, Alphonso de Spina was for many years superior of the House of Studies of the Friars Minor at Salamanca, and in 1491 was created Bishop of Thermopylae in Greece. Recent scholarship suggests that Alphonso was not a converted Jew or converso. He was a man of great learning and attained considerable renown as a preacher, but his chief claim to fame is as the author of Fortalitium Fidei, sometimes just called the Fortalitium.