Once upon a time, when the gods were building their abodes, a certain builder came and offered to erect them, in the space of three half-years, a city so well fortified that they should be quite safe in it from the incursions of the forest-giants and the giants of the mountains, even although these foes should have already penetrated within the enclosure Midgard. He asked, however, for his reward, the goddess Freyja, together with the sun and moon. The gods thought over the matter a long while, and at length agreed to his terms, on the understanding that he would finish the whole work himself without any one’s assistance, and that all was to be finished within the space of one single winter. If anything remained to be done when the first day of summer came, the builder was to entirely forfeit the reward agreed on. When the builder was told this he asked that he might be allowed the use of his horse, Svadilfari, and to this the gods, by the advice of Loki, agreed.
On the first day of winter the builder set to work, and during the night he caused his horse to draw stones for the building. The gods beheld with astonishment the extraordinary size of these, and marked with wonder that the horse did much more work than his master. The contract between them and the giant had, however, been confirmed with many oaths and in the presence of many witnesses, for without such a precaution a giant would not have trusted himself among the gods, especially at a time when Thor was returning from an expedition he had made into the east against the giants.
The winter was far advanced, and towards its end the city had been built so strongly and so lofty as to be almost secure. The time was nearly expired, only three days remaining, and nothing was wanted to complete the work save the gates, which were not yet put up. The gods then began to deliberate, and to ask one another who it was that had advised that Freyja should be given to one who dwelt in Jotunheim, and that they should plunge the heavens in darkness by allowing one to carry away with him the sun and moon. They all agreed that only Loki could have given such bad counsel, and that it would be only just to either make him contrive some way or other to prevent the builder accomplishing his work and having a right to claim his reward, or to put him to death. They at once laid hands on Loki, who, in his fright, promised upon oath to do what they desired, let it cost him what it might.
That very night, while the builder was employing his horse to convey stones, a mare suddenly ran out of a neighbouring forest and commenced to neigh. The horse broke loose and ran after the mare into the forest, and the builder ran after his horse.
Between one thing and another the whole night was lost, so that when day broke the work was not completed.
The builder, recognising that he could by no means finish his task, took again his giant form; and the gods, seeing that it was a mountain-giant with whom they had to deal, feeling that their oath did not bind them, called on Thor. He at once ran to them, and paid the builder his fee with a blow of his hammer which shattered his skull to pieces and threw him down headlong into Niflhel.
The horse Sleipner comes of the horse Svadilfari, and it excels all others possessed by gods or men.