Almost everything popularly known about pre-Christian Uppsala comes from a few paragraphs written around 1075 by Adam of Bremen, a cleric who had not been there and who was writing about the mission field of his own archbishopric. He describes a temple entirely covered in gold, holding three images with Thor in the middle and Odin and Fricco beside him, priests assigned to each, and a festival every nine years at which nine males of every living kind were sacrificed and hung in a grove beside the building, with a note that a Christian informant had seen the bodies. A tree that never lost its leaves and a spring for drowning offerings complete the picture.
The account has to be read for what it is: a hostile description of a rival religion, written to justify a mission, by an author who says himself that he had it from others. Archaeology at Gamla Uppsala has found large royal burial mounds, a great hall on a terrace, and long rows of massive posts running across the site, but no building matching Adam's temple has been identified beneath the medieval church.
What is not in doubt is that the place was a centre of royal power and public assembly for the Svear, with a thing that met there and mounds raised over cremation burials containing gold, glass and imported goods. The atlas records Adam's temple as reported rather than established, and the mounds and the assembly as attested.