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:
Narikala is an ancient fortress overlooking Tbilisi, the capital of Georgia, and the Kura River. The fortress consists of two walled sections on a steep hill between the sulphur baths and the botanical gardens of Tbilisi. On the lower court there is the recently restored St Nicholas church. Newly built in 1996–1997, it replaces the original 13th-century church that was destroyed in a fire. The new church is of 'prescribed cross' type, having doors on three sides. The internal part of the church is decorated with the frescos showing scenes both from the Bible and history of Georgia.
The fortress was established in the 4th century and it was a Persian citadel. It was considerably expanded by the Umayyads in the 7th century and later, by king David the Builder (1089–1125). Most of extant fortifications date from the 16th and 17th centuries. In 1827, parts of the fortress were damaged by an earthquake and demolished.