This same cause enlisted a contemporary genius, prolific beyond precedent, called by Cervantes "that great prodigy of Nature," Lope de Vega, who freely borrowed from it in a play entitled _Los Cautivos de Argel_. At a later day, Calderon, sometimes exalted as the Shakespeare of the Spanish stage, in one of his most remarkable dramas, _El Principe Constante_, cast a poet's glance at Christian slavery in Morocco. To these works, belonging to what may be called the literature of Anti-Slavery, and shedding upon our subject a grateful light, must be added a curious and learned volume on the Topography and History of Algiers (_Topographia e Historia de Argel_), by Haedo, a Spanish father of the Catholic Church, published in 1612, and containing also two copious Dialogues,--one on Captivity (_de la Captividad_), and the other on the Martyrs of Algiers (_de los Martyres de Argel_). These Dialogues, besides embodying authentic sketches of suffering in Algiers, form a mine of classical and patristic learning on the origin and character of slavery, with arguments and protestations against its iniquity, which may be explored with profit even in our day. In view of this gigantic evil, particularly in Algiers, and in the hope of arousing his countrymen to the generous work of emancipation, the good father exclaims, in words which must thrill the soul so long as a single fetter binds a single slave: "Where is charity? Where is the love of God? Where is the zeal for his glory? Where is desire for his service? Where is human pity, and the compassion of man for man? Certainly, to redeem a captive, to liberate him from wretched slavery, is the highest work of charity, of all that can be done in this world."[6] The reports of the good fathers who visited this land of bondage for the redemption of captives testify likewise. One of these thus speaks from the depths of the heart: "The charity of Jesus Christ obliges us; and I question not but that whosoever had seen those miseries I have been a witness to, and the deplorable condition I left our captives in, would have no less ardent a desire to relieve them."[7] [6] Pp. 140, 141. [7] Busnot, History of the Reign of Muley Ismael: Preface.