Heimskringla Tricks and Illusions

But when Óðinn heard that good land was available from Gylfi to
the east, he went there, and he and Gylfi came to terms, because Gylfi did
not think he had the power to withstand the Æsir. Óðinn and Gylfi often
competed in tricks and illusions, and the Æsir were always superior. Óðinn
established his dwelling by Lǫgrinn at the place now called Old Sigtúnir,
and built a large temple there and performed sacrifices according to the
custom of the Æsir. He took possession of lands over the whole area that he
gave the name Sigtúnir to. He gave dwelling places to the temple priests.


- Heimskringla, Ynglinga Saga, Chapter 5