This was the reward which the gods gave to courage. When a hero had gloriously lost his life, the Valkyries, the nine warrior daughters of Odin, brought his body up to Valhalla on their white horses that gallop the clouds. There they lived forever after in happiness, enjoying the things that they had most loved upon earth. Every morning they armed themselves and went out to fight with one another in the great courtyard. It was a wondrous game, wondrously played. No matter how often a hero was killed, he became alive again in time to return perfectly well to Valhalla, where he ate a delicious breakfast with the Jisir; while the beautiful Valkyries who had first brought him thither waited at table and poured the blessed mead, which only the immortal taste. A happy life it was for the heroes, and a happy life for all who dwelt in Asgard; for this was before trouble had come among the gods, following the mischief of Loki. This is how the trouble began. From the beginning of time, the giants had been unfriendly to the Æsir, because the giants were older and huger and more wicked; besides, they were jealous because the good Æsir were fast gaining more wisdom and power than the giants had ever known. It was the Æsir who set the fair brother and sister, Sun and Moon, in the sky to give light to men; and it was they also who made the jewelled stars out of sparks from the place of fire. The giants hated the Æsir, and tried all in their power to injure them and the men of the earth below, whom the Æsir loved and cared for. The gods had already built a wall around Midgard, the world of men, to keep the giants out; built it of the bushy eyebrows of Ymir, the oldest and hugest of giants. Between Asgard and the giants flowed Ifing, the great river on which ice never formed, and which the gods crossed on the rainbow bridge. But this was not protection enough. Their beautiful new city needed a fortress. So the word went forth in Asgard: "We must build us a fortress against the giants; the hugest, strongest, finest fortress that ever was built." Now one day, soon after they had announced this decision, there came a mighty man stalking up the rainbow bridge that led to Asgard city. "Who goes there!" cried Heimdal the watchman, whose eyes were so keen that he could see for a hundred miles around, and whose ears were so sharp that he could hear the grass growing in the meadow and the wool on the backs of the sheep. "Who goes there! No one can enter Asgard if I say no." "I am a builder," said the stranger, who was a huge fellow with sleeves rolled up to show the iron muscles of his arms. "I am a builder of strong towers, and I have heard that the folk of Asgard need one to help them raise a fair fortress in their city."