 This kind of purple-red and white glass has otherwise only been found at St. Denis in Paris, in Italian Pavia, and in Birka near Stockholm.Around the year 1220, the then reigning lord of the region erected a fortified tower in order to protect the imperial highway at the toll station in Horrenberg.For the location of the fort, they chose a hill next to the highway which loomed a swampy low-lying section of the Leimbach.