The Divine Comedy is divided into three parts or books, _canticas_, as they are called by Dante: Hell, Purgatory, and Paradise, each one containing thirty-three cantos, with one additional introductory canto prefixed to the Hell. Even the number of lines in the three _canticas_ is approximately the same.[7] Dante's love for number-symbols was shown in the New Life, hence we are justified in accepting the theory that the threefold division of the poem is symbolical of the Trinity, and that the thirty-three cantos of each _cantica_ represent the years of the Savior's life. It is worthy of note that the last word in each of the three books is "stars." The allegory of the Divine Comedy has been the subject of countless discussions. The consensus of the best modern commentators seems to be, however, that although the allegory is more or less political, it is chiefly religious. The great theme is the salvation of the human soul, represented by Dante himself, who is the protagonist of the poem. As he wanders first through hell, he sees in all its loathly horrors the "exceeding sinfulness of sin," and realizes its inevitable punishment; as he climbs the steep slopes of purgatory, at first with infinite difficulty, but with ever-increasing ease as he approaches the summit, he learns by his own experience how hard it is to root out the natural tendencies to sin that pull the soul downward; and finally, as he mounts from heaven to heaven, till he arrives in the very presence of God Himself, he experiences the joy unspeakable that comes to him who, having purged himself of all sin, is found worthy to join "the innumerable company of saints and the spirits of just men made perfect." The Divine Comedy is a visionary journey through the three supernatural worlds, Hell, Purgatory, and Paradise. Such visions were by no means infrequent in the Middle Ages, and Dante had many predecessors. He simply adopted a poetical device well known to his contemporaries. What differentiated him from others is the dramatic and intensely personal character of his vision; the consummate skill with which he interwove into this one poem all the science, learning, philosophy, and history of the times; and the lovely poetry in which all these things are embalmed. To appreciate the vast difference between the Divine Comedy and previous works of a similar nature, we need only to read a few pages of such crude books as the Visions of Alberico, Tugdale, and Saint Brandon.