Neu-Thierstein Castle was founded in 1100 and a new building was built around 1294/95. The castle was apparently built by the Saugern-Pfeffingen family as a seat for a Kastvogtei (or a vogt with authority over a religious structure) who ruled over Beinwil Abbey. The first mention of the castle comes from 1321 when it was called Bello. As heirs of the Saugern-Pfeffingen family, in the late 12th Century, the count of Thierstein took over the castle and the Kastvogtei post. By 1400 it was known as Thierstein Castle. The castle was occupied by the Canton of Solothurn in 1445, 1467 and 1499. After the extinction of the counts of Thierstein in 1522, Solothurn acquired the castle and made it the administrative center of the secular bailiwick of Thierstein. In 1798 the castle was sold for demolition. However, in the 19th Century, the destruction of the castle are stopped by private individuals who wanted to repair the ruins. The ruins were surveyed and archeologically investigated in 1985.
The castle ruins are on a small rocky outcrop above the municipality of Büsserach. The ruin consists of a residential tower with ancillary buildings. Traces of a bailey and the old gate house on the south side can still be seen.
References:The Walls of Constantinople are a series of defensive stone walls that have surrounded and protected the city of Constantinople (today Istanbul) since its founding as the new capital of the Roman Empire by Constantine the Great. With numerous additions and modifications during their history, they were the last great fortification system of antiquity, and one of the most complex and elaborate systems ever built. They were also the largest and strongest fortification in both the ancient and medieval world.
Initially built by Constantine the Great, the walls surrounded the new city on all sides, protecting it against attack from both sea and land. As the city grew, the famous double line of the Theodosian Walls was built in the 5th century. Although the other sections of the walls were less elaborate, they were, when well-manned, almost impregnable for any medieval besieger.