Research identifies medieval tunnel under Szczecin’s Ducal Castle

Scientific testing showed that a medieval brick tunnel discovered under Ducal Castle in Szczecin during the excavation of a WWII tunnel in June 2020 had in fact been constructed in the Middle Ages.

The 270-metre long tunnels from the WWII period located under the northern slope of Castle Hill were discovered during research carried out before the modernisation of the Ducal Castle terraces in June 2020.

Castle director Barbara Igielska said: “We made a preliminary inventory. It turns out that we have 270 metres of this tunnel, but the reinforced concrete tunnel turns into a brick tunnel. We handed over the brick and mortar samples for testing... and it turned out that both the brick and the mortar were medieval.”

She went on to say that “the reinforced concrete tunnel is in good condition. But we are worried about the medieval tunnel. We are concerned about how it will react to changes in humidity when the entrances to the tunnels are opened."

The research, during which the German tunnel was discovered, was connected to recommendations after a construction disaster in 2017, when a pillar in the north wing of the structure and the ceiling collapsed.

Head of the investment and renovation department of Ducal Castle, Karol Krempa, said: “Initial exploration reveals a more complex issue than we originally thought regarding the extent and shape of these tunnels. 270 running metres of tunnels (are located) under the northern wing, the northern terrace and the slope: 210 m under the terrace and slope, 60 m under the northern wing, including a 25 m long brick tunnel."

He added that the prefabricated German tunnels are “identical to the tunnels that we discovered during investments” in Szczecin, while “disturbing phenomena” was observed in the brick tunnels.

“These tunnels now form a privileged runoff for groundwater from the courtyard, from the entire hill, and therefore we must urgently intervene. Above all, we must let experts in,” he said.

For further research and construction work to be carried out, it is necessary to unblock two entrances at the foot of the escarpment.

Mr Krempa went on to say that “there are many sinkholes in these tunnels. We do not know whether they are anthropogenic or natural sinkholes. Experts will answer this question. We also do not rule out that the 270 metres in which we are moving at the moment, may be part of an even greater system."

Ducal Castle in Szczecin is a Renaissance building located near the Oder river; it was the historical seat of the dukes of Pomerania-Stettin of the House of Pomerania (Griffins), who ruled the Duchy of Pomerania.

It was extensively damaged during Allied air raids in 1944 and rebuilt in 1958-80.

Currently, it houses the Ducal Castle cultural centre, the Castle Opera, the wedding hall of the Registry Office and the seat of the Marshal's Office.