(1) _On Abstinence from the Flesh of Living Beings_,[76] in four books, addressed to a certain Firmus Castricius, a Pythagorean, who for some reason or other had become a renegade to the principles, or at least to the practice, of his old faith. Next to the inculcation of abstinence as a spiritual or moral obligation, Porphyry’s “chief object seems to have been to recommend a more spiritual worship in the place of the sacrificial system of the pagan world, with all its false notions and practical abuses. This work,” adds Dr. Donaldson, “is valuable on many accounts, and full of information.” (2) His criticism on Christianity, which he entitled a _Treatise against the Christians_--his most celebrated production. It was divided into fifteen books. All our knowledge of it is derived from Eusebius, Jerome, and other ecclesiastical writers. Several years after its appearance the courtly Bishop of Cæsarea, the well-known historian of the first ages of Christianity, replied to it in a work extending to twenty-five books. More than a century later, Theodosius II. caused the obnoxious volume to be publicly burned, and Porphyry’s criticism shared the fate of those “many elaborate treatises which have since been committed to the flames” by the theological or political zeal of orthodox emperors and princes.[77] (3) _The Life of Pythagoras_--a fragment, but, as far as it goes, the most interesting of the Pythagorean biographies. (4) _On the Life of Plotinus and the Arrangement of his Works._ It is to this biography we are indebted for our knowledge of the estimable elaborator of New-Platonism. We learn that he was the pupil of Ammonius, who disputes with Numenius the fame of having originated the principles of the new school of thought of which Plotinus, however, was the St. Paul--the actual founder. Of a naturally feeble constitution, he had early betaken himself to the consolations of divine philosophy. After vainly seeking rest for his truth-loving and aspiring spirit in other systems, he at last found in Ammonius the teacher and teaching which his intellectual and spiritual sympathies demanded. His great ambition was to visit the country of Buddha and of Zerdusht or Zoroaster, and, for that purpose, he joined the expedition of the Emperor Gordian against the Persians. The defeat and death of that prince frustrated his plans. He then settled at Rome, where he established his school, and he remained in Italy until his death in 270. By the earnest solicitations of his disciples, Porphyry and Amerius, he was induced with much reluctance to publish his oral discourses, and eventually they appeared in fifty-four books, edited by Porphyry, who gave them the name of the _Enneads_, as being arranged in six groups of _nine_ treatises. Perhaps no teacher ever engaged to so unbounded an extent the admiration and affection of his followers.