We all know of the Alzette river, but have you ever traced its journey from the source in France to the Sauer river near Ettelbruck? Olivier Catani has done just that.

RTL Today has teamed up with PISA, the Luxembourgish science magazine, to reproduce their original videos in English for our site. Presenter Olivier Catani takes you to the Alzette river this week, exploring its history, hidden tunnels and how it takes you through the remains of Luxembourg City's fortress.

This video is part of the PISA series for RTL Today. Watch all English videos on RTL Play, or discover the wide range of subjects previously covered in Luxembourgish here (there are 13 seasons, mind you! We'll try and catch up...). Our previous episodes covered the history of the tramLuxembourg airport, explained how the coronavirus vaccine works, asked why traffic lights always seem to be red, investigated where our tap water comes from, looked at Luxembourg's railways since 1859, took a dive into the Moselle Valley and its underground Dolomite mines and more...

Birth in France

The Alzette pond in France is the source of the river, just a few kilometres across the border. The water is beautifully clear - in comparison to the river. The river flows from this pond in Thill through Esch-sur-Alzette to Luxembourg City, Mersch and Ettelbruck.

After a few hundred metres, the river suddenly disappears into a dark pipe. As with many rivers, the Alzette has been canalised, and it even starts underground in Luxembourg as well. The limestone in the canal is washed out of the concrete, only to crystalise again, just like a cave.

The Alzette river was taken out of its natural riverbed and channeled to Rue de l'Alzette. For the city to expand, the river had to be taken underground and diverted. In the video, Olivier would like to walk through the canal, but due to the bad air quality this is not recommended.

Water powered mills of Luxembourg City

The river looks much prettier in Luxembourg's old town. It proved to be a vital river for locals in the past, as it powered industrial facilities dotted along the water. There is still one mill one can visit, part of the Luxembourg City History Museum. The mill in fact produced mustard - up to 1,000kg of seeds could be pressed per day.

Today, the Alzette is still harnessed to power a number households.

Finally, Olivier also visits a chamber below Boulevard de Kockelscheuer that fills up in case of heavy rain. All new residential areas must be built with such retention basins. Once it stops raining, the basin is drained.