Asgard, a realm of wonders, was where  the Norse Gods made their home. There Odin’s great hall of Valhalla  towered above the mountains and Bifrost, the rainbow bridge,  anchored itself. But though their domain was magnificent, it stood undefended from the giants  and trolls of Jotunheim, who despised the gods and  sought to destroy them. One day when Thor, strongest of the  gods, was off fighting these foes, a stranger appeared,  riding a powerful gray horse. The visitor made the gods  an astonishing offer. He would build them the greatest  wall they’d ever seen, higher than any giant could climb  and stronger than any troll could break. All he asked in return was the beautiful  goddess Freya’s hand in marriage— along with the sun and moon from the sky. The gods balked at this request  and were ready to send him away. But the trickster Loki  concocted a devious plan. He told the gods they should  accept the stranger’s offer, but set such strict conditions that he  would fail to complete the wall in time. That way, they would lose nothing, while  getting most of the wall built for free. Freya didn’t like this idea at all, but Odin and the other  gods were convinced and came to an agreement  with the builder. He would only have one winter  to complete the wall. If any part was unfinished by  the first day of summer, he would receive no payment. And he could have no help  from any other people. The gods sealed the deal with solemn oaths and swore the mason would come  to no harm in Asgard. In the morning, the stranger began to dig  the foundations at an astonishing speed, and at nightfall he set off towards the  mountains to obtain the building stones. But it was only the next morning,  when they saw him returning, that the gods began to worry. As agreed, no other people  were helping the mason. But his horse Svadilfari was hauling  a load of stones so massive it left trenches in the ground  behind them. Winter came and went. The stranger kept building,  Svadilfari kept hauling, and neither snow nor rain could  slow their progress. With only three days left until summer,  the wall stood high and impenetrable, with only the gate left to be built. Horrified, the gods realized that not  only would they lose their fertility goddess forever, but without the sun and moon the world  would be plunged into eternal darkness. They wondered why they’d made  such a foolish wager— and then remembered Loki  and his terrible advice. Suddenly, Loki didn’t feel so clever. All of his fellow gods threatened him  with an unimaginably painful death if he didn’t find some way to prevent  the builder from getting his payment. So Loki promised to take care of the  situation, and dashed away. Outside, night had fallen, and the builder prepared to set off  to retrieve the final load of stones. But just as he called Svadilfari to him,  a mare appeared in the field. She was so beautiful that  Svadilfari ignored his master and broke free of his reins. The mason tried to catch him, but the mare ran deep into the  woods and Svadilfari followed. The stranger was furious. He knew that the gods were behind  this and confronted them: no longer as a mild-mannered mason, but in his true form as a terrifying  mountain giant. This was a big mistake. Thor had just returned to Asgard, and now that the gods knew  a giant was in their midst, they disregarded their oaths. The only payment the  builder would receive— and the last thing he would ever see— was the swing of Thor’s  mighty hammer Mjolnir. As they set the final stones into the  wall, the gods celebrated their victory. Loki was not among them, however. Several months would pass  before he finally returned, followed by a beautiful gray  foal with eight legs. The foal would grow into a magnificent  steed named Sleipnir and become Odin’s mount, a horse  that could outrun the wind itself. But exactly where he had come from was  something Loki preferred not to discuss.