The Arch of Hadrian is a monumental gateway resembling – in some respects – a Roman triumphal arch. It spanned an ancient road from the center of Athens, to the complex of structures on the eastern side of the city that included the Temple of Olympian Zeus. It has been proposed that the arch was built to celebrate the adventus (arrival) of the Roman Emperor Hadrian and to honor him for his many benefactions to the city, on the occasion of the dedication of the nearby temple complex in 131 or 132 AD.
It is not certain who commissioned the arch, although it is probable that the citizens of Athens or another Greek group were responsible for its construction and design. There were two inscriptions on the arch, facing in opposite directions, naming both Theseus and Hadrian as founders of Athens. While it is clear that the inscriptions honor Hadrian, it is uncertain whether they refer to the city as a whole or to the city in two parts: one old and one new. The early idea, however, that the arch marked the line of the ancient city wall, and thus the division between the old and the new regions of the city, has been shown to be false by further excavation.
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Sigmaringen Castle was first mentioned in the year 1077 in the chronicles of Petershausen monastery. The oldest parts of the castle are concealed beneath the alterations made during the 17th and the 19th centuries. The secret of the earliest settlement built on this defendable rock will never be fully revealed: large-scale excavation work would be necessary, which the extensive land development renders impossible. Judging from the many Roman remains unearthed in the area around Sigmaringen, the 12th century keep known as the 'Roman Tower' could be traced back to a Roman predecessor.
The castle remains that have been preserved (gate, great hall and keep) date back to the Staufer period around 1200. The castle remains were integrated into subsequent buildings. The foundations of the castle buildings are to a large extent identical to the surrounding castle wall.
These remains give us a good idea of how the castle might have looked during the 12th century.