And all the while the King of Elfland watched; for he knew by magic when Alveric's sword drew near: it had troubled his kingdom once, and the King of Elfland knew well the flavour of thunderbolt iron when he felt it loom on the air. From this he had withdrawn his frontiers far, leaving all that ragged land deserted of Elfland; and though he knew not the length of human journeys, he had left a space that to cross would weary the comet, and rightly deemed himself safe. But when Alveric with his sword was far to the North the Elf King loosened the grip with which he had withdrawn Elfland, as the Moon that withdraws the tide lets it flow back again, and Elfland came racing back as the tide over flat sands. With a long ribbon of twilight at its edge it floated back over the waste of rocks; with old songs it came, with old dreams, and with old voices. And in a while the frontier of twilight lay flashing and glimmering near the fields we know, like an endless Summer evening that lingered on out of the golden age. But bleak and far to the North where Alveric wandered the limitless rocks still heaped the desolate land; only to fields from which he and his sword and his adventurous band were remotely gone that mighty inlet of Elfland came lapping back. So that close again to the leather-worker's cottage and to the farms of his neighbours, a bare three fields away, lay the land that was heaped and piled with all the wonder for which poets seek so hard, the very treasury of all romantic things; and the Elfin Mountains gazed over the border serenely, as though their pale-blue peaks had never moved. And here the unicorns fed along the border as it was their custom to do, feeding sometimes in Elfland, which is the home of all fabulous things, cropping lilies below the slopes of the Elfin Mountains, and sometimes slipping through the border of twilight at evening when all our fields are still, to feed upon earthly grass. It is because of this craving for earthly grass that comes on them now and then, as the red deer in Highland mountains crave once a year for the sea, that, fabulous though they are on account of their birth in Elfland, their existence is nevertheless known among men. The fox, which is born in our fields, also crosses the frontier, going into the border of twilight at certain seasons; it is thence that he gets the romance with which he comes back to our fields. He also is fabulous, but only in Elfland, as the unicorns are fabulous here.