In front of Landstingsborgen "the county council fort/castle", on Frösön, one finds Frösöstenen, often credited as the northernmost runestone of Sweden, albeit perfectly true, that is somewhat of an understatement, as it's the northernmost raised runestone in the entire world.
This runestone from about 1030-1050 AD, is unique in several regards, not only is it located in the far north of the then norse/viking cultural sphere, but it's the only one of it's kind in the region, one of three runic recordings of the conversation to Christianity (the sole mentioning the christening of a land), the name of Jämtland (Jamtaland) appears for the first time in history on it and the text has been identified as ancient Jamtish/Jamtlandic, thus making it the local dialect's oldest written document. Moreover the text is interpreted by some as supporting the notion of Jämtland as an independent entity in the period and it has been speculated that 'Austmaðr' was a cheiftain of the local Germanic thing Jamtamot. Furthermore, the serpent depicted on it, biting its own tail, is according to legend the Great-Lake Monster, Storsjöodjuret.
The inscription is (in English): Austmaðr, Guðfastr's son, had this stone raised and this bridge built and Christianised Jamtaland. Ásbjörn built the bridge. Trjónn and Steinn carved these runes.