Svadilfur in Norse mythology, was a famous horse of the giant who built the castle of the gods. He projected a great fortress for the asas who were defending themselves against the ice-giants; and he offered himself as an architect to erect it, provided they would give him three winters to finish it, and the beautiful Freia as a wife and the sun and moon as servants. By the advice of Loke, the asas accepted the offer, on the condition that he should fulfill it in one winter, and without any other help than the horse Svadilfur. The giant agreed to this, and his horse exhibited such extraordinary strength that he easily lifted stones of the greatest weight, which would have required a hundred horses to carry; and the building was already completed, except a single gate, before the asas had thought it possible. They then threatened Loke with death if he did not break up the contract. Loke thereupon assumed the form of a beautiful mare, and so engaged the stallion Svadilfur that he broke the rope by which he was held and followed Loke, who took him far enough away From this connection sprang Odin's famous eight-footed horse Sleipner, who was fleeter than the wind and never tired. The architect saw himself deserted by his help, and sought to assume his gigantic form in order to finish the work with all his strength; but in the dilemma of the gods as to whether in that case they should abide by their word, or whether the giant should not be required to finish the work as he was, Thor suddenly appeared with his hammer and slew the giant.