To enter into details on the Celtic religion would carry us beyond due limits. The question as to whether the ancient Celts were idolaters or not still remains undecided, though in France alone more than six hundred volumes have been written on the subject. Julius Caesar believed that they were worshippers of idols in the same sense as his own countrymen; but he probably stood alone in his opinion. Aristotle, Pythagoras, Polyhistor, Ammianus Marcellinus, considered the Druids as monotheist philosophers. Most of the Greek writers agreed with them, as did all the Alexandrian Fathers of the Church in the third and fourth centuries. Among the moderns the majority leans to a contrary opinion; nevertheless, many authors of weight, distinguishing the public worship of the common people from the doctrine of the Druids, assert the monotheism of this sacerdotal caste. Samuel F. N. Morus particularly, who, with J. A. Ernesti, was esteemed the master of antiquarian scholarship in Europe during the last century, maintains, in his edition of the "Commentaries" of Caesar, that "human beings, as well as human affairs, fortunes, travels, and wars, were thought by the Celts to be governed and ruled by one supreme God, and that the system of apotheosis, common to nearly all ancient nations, was totally unknown in ancient Gaul, Britain, and the adjacent islands." The ancient authorities concurring with these conclusions are so numerous and clear spoken that the great historian of Gaul, Amedee Thierry, thinks that such a pure and mystic religion, joined to such a sublime philosophy, could not have been the product of the soil. In his endeavor to investigate its origin, he supposes that it was brought to the west of Europe by the Eastern Cymris of the first invasion; that it was adopted by the higher classes of society, and that the old idolatrous worship remained in force among the lower orders. The unity and omnipotence of the Godhead, metempsychosis, or the doctrine and the transmigration of soul --not into the bodies of animals, as it obtained and still obtains in the East, but into those of other human beings--the eternal duration of existing substances, material and spiritual, consequently the immortality of the human soul, were the chief dogmas of the Druids, according to the majority of antiquarians. If this be true, then it can be said boldly that, with the exception of revealed religion in Judea, which was always far more explicit and pure, no system can be found in ancient times superior to that of the Druids, more especially if we add that, in addition to religious teaching, a whole system of physics was also developed in their large academies. "They dispute," says Caesar, "on the stars and their motions, on the size of the universe and of this earth, on the nature of physical things, as well as on the strength and power of the eternal God."