A castle in Arbon is first mentioned in 720 in a history of St. Gall Abbey. It stood on or near the site of the Roman era Arbor Felix fortress from 250 AD. After the Romans retreated south of the Alps around 400, the old fortress was abandoned. Sometime later a Frankish castle was built in Arbon probably for the Frankish royal family. By around 700, Arbon and presumably the castle, were the property of the diocese of Constance and an ecclesiastic overseer or bailiff ruled over Arbon.
The oldest part of the current castle is a 13th-century, originally free standing, residential tower. The tower may have been built on the foundation of an earlier building. The lower walls are up to 3.2 meters thick. Inside the castle there are two Romanesque fireplaces. In 1515-20 the Bishop Hugo von Hohenlandenberg rebuilt the castle to its current appearance. The old tower was rebuilt into a U shape. The upper most story, the gables and the hip roof are also from this reconstruction. The outer wall of the castle moved to stand exactly over the north-west corner of the Roman era fortress.
In 1822 the Stoffel silk ribbon weaving company moved into the castle. They remained there until 1907. In 1911 the castle was bought by Adolph Saurer, the founder of Adolph Saurer AG. He built workshops around the castle building as he experimented with motors, trucks and machinery. In 1944 his son, Hippolyt Saurer sold the castle to the city. The city renovated and expanded the castle and in 1967 opened the Historisches Museum Arbon (Arbon History Museum).References:
Roman Walls of Lugo are an exceptional architectural, archaeological and constructive legacy of Roman engineering, dating from the 3rd and 4th centuries AD. The Walls are built of internal and external stone facings of slate with some granite, with a core filling of a conglomerate of slate slabs and worked stone pieces from Roman buildings, interlocked with lime mortar.
Their total length of 2117 m in the shape of an oblong rectangle occupies an area of 1.68 ha. Their height varies between 8 and 10 m, with a width of 4.2 m, reaching 7 m in some specific points. The walls still contain 85 external towers, 10 gates (five of which are original and five that were opened in modern times), four staircases and two ramps providing access to the walkway along the top of the walls, one of which is internal and the other external. Each tower contained access stairs leading from the intervallum to the wall walk of town wall, of which a total of 21 have been discovered to date.
The defences of Lugo are the most complete and best preserved example of Roman military architecture in the Western Roman Empire.
Despite the renovation work carried out, the walls conserve their original layout and the construction features associated with their defensive purpose, with walls, battlements, towers, fortifications, both modern and original gates and stairways, and a moat.
Since they were built, the walls have defined the layout and growth of the city, which was declared a Historical-Artistic Ensemble in 1973, forming a part of it and becoming an emblematic structure that can be freely accessed to walk along. The local inhabitants and visitors alike have used them as an area for enjoyment and as a part of urban life for centuries.
The fortifications were added to UNESCO"s World Heritage List in late 2000 and are a popular tourist attraction.