Specifically, it is a natural stone wall of the sluice. ‘Not the sluice gate, but the wall of the sluice channel, which is a kind of canal that drained water outside the dike to the Maas’, explains archaeologist Patrick Ploegaert from the Municipality of Rotterdam. ‘That wall was a reinforcement of the bank. It was done with natural stone because it was wear-resistant and looked nice.’

Surprise

The archaeologists found this sluice wall in 2024, during the excavations at the site where the Rotta Nova residential tower is to be built. ‘It was already known from historical sources that there were sluices here’, says Ploegaert. ‘And during the Second World War, they were really excavated when the city center was still largely in ruins after the bombing. But most of the sluices were also removed at that time. Therefore, it was still a surprise that we found this wall now.’ 

A piece remains

Ploegaert says that archaeologists prefer to leave such finds in the ground. ‘Because they are better preserved there than when you remove them. But for the construction of Rotta Nova, this wall, 19 meters long and 3 meters high, must be mostly removed. Only the bottom meter can remain. That is interesting for future generations of archaeologists. They may have new techniques and insights for even better research.’

Carefully chip away

Three archaeologists will do the work, together with someone from the contracting company. How does that work? ‘We will chip them away piece by piece, but carefully of course’, laughs Ploegaert. ‘The stones are about 20 by 30 to 40 cm and weigh about 20 kilos. When the wall was built in the 15th century, they did not have cement yet. They used a kind of lime mortar, which fortunately is much softer.’  

Origin of natural stone 

Meanwhile, the archaeologists are also searching for ‘stonemasons’ marks’. ‘A kind of quality mark that the stonemasons used to put in their stones. We already know that this natural stone came from Belgium, but such a mark hopefully tells more details about the origin.’ 

The stones will be temporarily stored at a location of the municipality. The intention is to reuse them in a beautiful way at Rotta Nova. How exactly is not yet clear; the municipality will consider this in the coming years.

Name

The sluice is named Zevenhuizersluis. ‘In the Middle Ages, all small places along the Rotte had to contribute to the sluices’, says Ploegaert. ‘In return, the sluices were named after these ‘crafts’. This one happened to be named after the craft Zevenhuizen.’

The work is expected to last from Wednesday, March 18 to Friday, March 20. After that, the archaeological research is definitively completed. The excavation lasted half a year. In addition to the sluices, numerous other finds were made, such as bones, pottery, leather, and metal.