It resulted, from this extraordinary and most perilous power of oratory in ancient times, that the attention bestowed throughout life, but especially in youth, on training to excellence in it, was unbounded. In truth, education with them was so much directed to the study and the practice of oratory, that it formed in most of their academies the main object of instruction. Other topics--philosophy, poetry, science, mathematics, history--were not neglected, but they were considered chiefly as _subordinate to oratory_--rather, they were the preparatory studies, from which a perfect orator was to be formed. Cicero says expressly, that there is no subject of human knowledge of which the orator may not avail himself, in his public address, and which may not serve to enlighten his narrative, strengthen his argument, or adorn his expression.[23] This shows how lofty was the idea which he had formed of this noble art, and the aids which he was fain to obtain for it, from all, even the most dissimilar, branches of human knowledge. The greatest orators and philosophers of antiquity devoted themselves to instruction in its principles, and consideration of the manner of cultivating it with the highest success. Demosthenes taught, as every schoolboy knows, for a talent: a sum above £200, and equal to at least £500 in modern times. Cicero has left several beautiful treatises on oratory; Isocrates owes his fame mainly to his writings on the same subject; Quintilian has bequeathed to us a most elaborate work on its principles, and the mode of its instruction; the treatise of Aristotle on oratory is not the least celebrated of his immortal works. So vast was the number, and so great was the influence of the schools of rhetoric, that they came, in the later days of antiquity, to supersede almost every other subject of study; they attracted the ingenious youth from every part of the world to the groves of the Academy, and singly supported the prosperity and fame of Greece, for centuries after they had sunk under the withering grasp or declining fortunes of the Byzantine empire.