Then said Ganglere: A good ship is Skidbladner, but much black art must have been resorted to ere it was so fashioned. Has Thor never come where he has found anything so strong and mighty that it has been superior to him either in strength or in the black art? Har answered: Few men, I know, are able to tell thereof, but still he has often been in difficult straits. But though there have been things so mighty and strong that Thor has not been able to gain the victory, they are such as ought not to be spoken of; for there are many proofs which all must accept that Thor is the mightiest.

- Prose Edda (The Fooling of Gylfe, XIV)