Tinnumburg is the best preserved of the three ancient ring forts in Sylt. The fort was built around the birth of Christ. The rampart has a diameter of 120 meters. The wall is up to seven meters high and has a circumference of about 440 meters. The castle had at least two gates (east and south).
Excavations in 1870, 1948 and 1976 provided evidence that the Tinnumburg was built in the style of early Roman Empire round ramparts on the North Frisian islands. The excavations have shown that this is a Germanic site of worship. The fort was in use again in the 8th to 10th centuries.References:
Frösöstenen is the northern-most raised runestone in the world and Jämtland's only runestone. It originally stood at the tip of ferry terminal on the sound between the island of Frösön and Östersund. The stone dates to between 1030 and 1050. It has now been relocated to the lawn in front of the local county seat due to the construction of a new bridge, between 1969 and 1971, on the original site.
Frösö runestone inscription means: Austmaðr, Guðfastr's son, had this stone raised and this bridge built and Christianized Jämtland. Ásbjörn built the bridge. Trjónn and Steinn carved these runes.