Frohburg Castle

Trimbach, Switzerland

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Frohburg Castle is a large medieval castle ruin situated on a hill near Trimbach in the canton of Solothurn, Switzerland, built around the 10th or 11th century by the noble House of Frohburg, who used it as their primary stronghold to control lands between the Aare and Rhine rivers.

The site reached its peak as a power center in the 12th and 13th centuries, with the family founding towns like Olten and Zofingen before their line divided into branches and declined, selling possessions to the Habsburgs and others by 1367.

Recognized as a Swiss heritage site of national significance, the ruins feature remnants of walls, service buildings, and water cisterns, accessible year-round via hiking paths with no entrance fee, and archaeological digs since the 1970s have uncovered evidence of iron smelting and medieval trades.