The Hölstein Mosaic was discovered by chance in 1946 during a search for a water source in Hölstein, in the canton of Basel-Landschaft. It adorned the floor of a bathhouse on a 2nd-century AD Roman estate.

The mosaic, which measures approximately 15 square meters, features a geometric, checkerboard-like pattern on the outer edges. In the central medallion, a colorful floral design unfolds with a flower in the center, surrounded by a frieze of bell-shaped blossoms and heart-shaped leaves. The composition resembles an artistically designed tapestry.

Why is the mosaic on display at the Roman house?

The estate in “Hinterbohl” in Hölstein is one of the oldest rural settlements in the vicinity of Augusta Raurica. Such estates supplied the urban population with agricultural products and were closely linked to it both economically and socially. That is why the mosaic is now appropriately displayed in the Roman house at Augusta Raurica.

How did the mosaic end up here?

After the mosaic was excavated in 1947, it was decided to backfill the exposed architectural structures once they had been documented, but to preserve the mosaic. It was encased in plaster, lifted from the ground in two pieces, transported to Augst by horse-drawn carriage, and restored. Since the 1950s, the mosaic has been on display in the dining hall (oecus) of the Roman house.

The excavations also brought to light other finds, such as a statuette of Mercury, wall paintings, and an iron window grille.

Restoration 2025 – How is a mosaic restored?

Archaeological artifacts such as this mosaic in the Roman house can remain preserved in the ground for thousands of years. Once they are excavated, they come into contact with their environment – people, the surrounding air, wind and weather, as well as other structural processes that can damage the building fabric and materials. To preserve the Hölstein mosaic for future generations, it underwent extensive restoration in 2025.

First, we researched the history of its discovery and previous restorations. This is necessary to understand whether older restoration materials – which were used at the time to the best of the experts’ knowledge and belief – are now causing damage and may need to be replaced. It turned out that a wide variety of restoration mortars with different properties had been used – including lime, cement, and acrylates. Since these mortars all have different degrees of hardness, they create stresses that can lead to cracks in the mosaic floor. The smooth, polished surface is also a result of earlier interventions.

The current condition was then assessed. Damage such as cracks, loose tesserae (mosaic tiles), or hollow spots was mapped. This mapping serves to document the condition prior to restoration and to visualize damage processes.

During restoration, damaged joints were filled with a suitable lime mortar, and loose mosaic tiles were reattached. Older, problematic cement mortars were partially removed, and the affected tiles were reinserted.

Rock-hard? – The mosaic as a fragile structure

The restoration revealed that much of the damage is attributable to heavy foot traffic over the past decades.

The limestone from which the mosaic tiles are made is sensitive to moisture and mechanical stress. However, the floor’s construction is particularly vulnerable: the mosaic is set in a steel frame that is not firmly attached to the subfloor. Foot traffic creates vibrations that cause the mosaic tiles to shift, the mortar layers to detach, and small voids to form.

The heavier the use, the greater the strain. In the long term, the valuable ancient mosaic floor risks disintegrating into its individual parts.

We are currently exploring how to protect the mosaic sustainably while ensuring that visitors can still access the triclinium’s niches – a challenge that exemplifies modern heritage conservation.

Until further notice, the dining hall in the Roman house will remain closed. This will ensure that the mosaic is preserved for future visitors.