The Ruins of Farnsburg Castle and the Roman Temple at Grienmatt

4 October 2026

The ruins of Farnsburg Castle (Canton of Basel-Landschaft), near the villages of Buus, Ormalingen and Magden, and the ruins of the Roman temple at Grienmatt near Kaiseraugst (Canton of Aargau) are located less than five kilometres apart.

The Lords of Farnsburg, however, were unaware of this Roman temple. Likewise, the inhabitants of this first Roman city ( Colonia Augusta Raurica) in what is now Switzerland were not aware of a castle at Farnsburg. After all, they could not see into the future. And yet the two sites have several things in common: not only the River Ergolz, but also the history of this region of the cantons of Aargau and Basel-Landschaft, the rule of the Habsburgs and the city of Basel.

Augusta Raurica, Augst and Kaiseraugst

Kaiseraugst takes its name from the Colonia Augusta Raurica. After the Romans withdrew in the 5th century, this Roman city of 15,000 inhabitants fell into decline. By around 1300, it had become a village called Augst, with a few hundred inhabitants and Roman ruins that were used as a quarry. The River Ergolz continued to flow through the village as it always had.

In the 3rd century, the Romans had built a fortress on the Rhine, on the eastern bank of the Ergolz, to protect the Limes, the Roman frontier. In 1461, the city of Basel acquired the western part of the village of Augst, while the Habsburgs took control of its eastern part and named it “Kaiseraugst” to distinguish it from Augst.

The Roman Temple at the Grienmatt

The large temple complex is thought to have measured approximately 200 metres in both length and width. Its central section, with a colonnade and altar, covered an area of approximately 125 by 132 metres. A bathhouse complex, or thermal baths, stood immediately beside it. It is believed to have been a nymphaeum or a Gallo-Roman double temple, associated with bathing facilities.

Today, it is difficult to imagine that this enormous complex did not stand in isolation in a meadow, but in the middle of the urban area of Augusta Raurica. Further east were the great theatre, the amphitheatre, the forum, the Curia, the basilica and, for example, the Schönbühl Temple.

Various streets, lined with statues, columns, altars and other structures, connected the temple with this part of Augusta Raurica. As numerous religious gatherings and festivities were held in honour of the emperor as part of the imperial cult, there were many processions on these streets.

Archaeological interest in the ruins of the temple at Grienmatt did not emerge until the 16th and 17th centuries. It was not until the 18th and 19th centuries, however, that its investigation became a matter of scientific research. Among the first scholars to study the site scientifically were Daniel Schöpflin (1694–1771) and Aubert Parent (1753–1835).

Today, the temple at Grienmatt forms part of the Augusta Raurica museum. Scientific research is still ongoing, and although not all questions have yet been resolved, the temple at Grienmatt was probably the most important temple complex in the Colonia Augusta Raurica.

Farnsburg Castle

A castle complex already stood on the rocky spur in the 12th or 13th century. The Counts of Thierstein expanded Farnsburg Castle between 1319 and 1342 and made it their residence. In 1418, Farnsburg came into the possession of the Counts of Falkenstein. The Habsburgs subsequently owned it for several years. In 1461, the city of Basel purchased the lordship.

Farnsburg subsequently became the seat of a bailiff, and numerous building works transformed it into a structure suited to the needs of the time. The castle was destroyed by the local population in 1798 following the French invasion and was subsequently used as a quarry.

The ruins, with their surviving and imposing shield wall (hence the name Schildmauerburg), were restored between 2019 and 2023. The Canton of Basel-Landschaft is notable for its high density of castles, but Farnsburg was once the queen of the region’s castles.

Conclusion

So what do these two ruins have in common that makes them worth discussing in the same article? Despite belonging to different eras, they are linked by their representation of power. In Augusta Raurica, this was expressed through the imperial cult; at Farnsburg, through the power of local rulers, followed for a short period by the Habsburgs and subsequently by the city of Basel.

Both places were under Habsburg rule, Farnsburg for a short period and Kaiseraugst for much longer. Both also experienced the direct consequences of the French Revolution and Napoleon’s invasion.

Farnsburg was destroyed in 1798. During the Helvetic Republic (1798–1803), Kaiseraugst was briefly incorporated into Augst before becoming part of the Canton of Aargau in 1803. After the Helvetic Republic, Farnsburg once again became part of the Canton of Basel, before being incorporated into the Canton of Basel-Landschaft in 1833. It is the fascinating history of Switzerland condensed into just a few square kilometres.