Explaining they are about to emerge at the antipodes of the spot where they entered Hades, where they will behold the great Western Sea, Virgil adds they will find in its centre the Mount of Purgatory, constructed of the earth displaced by Satan's fall. Thus, Dante and his leader return to the bright world, and, issuing from the dark passage in which they have been travelling, once more behold the stars! "By that hidden way My guide and I did enter, to return To the fair world: and heedless of repose We climb'd, he first, I following his steps, Till on our view the beautiful lights of heaven Dawn'd through a circular opening in the cave: Thence issuing we again beheld the stars." PURGATORY _Canto I._ About to sing of a region where human spirits are purged of their sins and prepared to enter heaven, Dante invokes the aid of the muses. Then, gazing about him, he discovers he is in an atmosphere of sapphire hue, all the more lovely because of the contrast with the infernal gloom whence he has just emerged. It is just before dawn, and he beholds with awe four bright stars,--the Southern Cross,--which symbolize the four cardinal virtues (Prudence, Justice, Fortitude, and Temperance). After contemplating these stars awhile, Dante, turning to the north to get his bearings, perceives Virgil has been joined in this ante-purgatorial region by Cato, who wonderingly inquires how they escaped "the eternal prison-house." Virgil's gesture and example have meantime forced Dante to his knees, so it is in this position that the Latin poet explains how a lady in heaven bade him rescue Dante--before it was too late--by guiding him through hell and showing him how sinners are cleansed in Purgatory. The latter part of Virgil's task can, however, be accomplished only if Cato will allow them to enter the realm which he guards. Moved by so eloquent a plea, Cato directs Virgil to wash all traces of tears and of infernal mirk from Dante's face, girdle him with a reed in token of humility, and then ascend the Mount of Purgatory,--formed of the earthy core ejected from Hades,--which he points out in the middle of a lake with reedy shores. Leading his charge in the early dawn across a meadow, Virgil draws his hands first through the dewy grass and then over Dante's face, and, having thus removed all visible traces of the passage through Hades, takes him down to the shore to girdle him with a pliant reed, the emblem of humility. _Canto II._ Against the whitening east they now behold a ghostly vessel advancing toward them, and when it approaches near enough they descry an angel standing at its prow, his outspread wings serving as sails. While Dante again sinks upon his knees, he hears, faintly at first, the passengers in the boat singing the psalm "When Israel went out of Egypt."