The prime material of the epic poet, then, must be real and not invented. But when the story of the poem is safely concerned with some reality, he can, of course, graft on this as much appropriate invention as he pleases; it will be one of his ways of elaborating his main, unifying purpose–and to call it unifying is to assume that, however brilliant his surrounding invention may be, the purpose will always be firmly implicit in the central subject. Some of the early epics manage to do without any conspicuous added invention designed to extend what the main subject intends; but such nobly simple, forthright narrative as Beowulf and the Song of Roland would not do for a purpose slightly more subtle than what the makers of these ringing poems had in mind.