Only a few steps away from the cathedral, the people of Cologne have been building a museum underground for years that is unlike any other in the world. They call it MiQua in reference to the mikvah. When it is finished at some point - no one knows when that will be - it will comprise a 600-metre-long tour that will lead from the ruins of the Roman governor's palace for Lower Germania - part of the Unesco World Cultural Heritage - through the medieval Jewish quarter. For all this has been uncovered by archaeologists underground. It has a high Indiana Jones content, the only difference being that here everything is real.

Behind high construction fences, a rickety ladder leads down into the long-submerged parallel world. Here the English archaeologist Gary White (66), a native of Portsmouth, waits, you have to imagine a similarity to Albus Dumbledore actor Michael Gambon. "This dig here covers 2000 years of history, you don't have that anywhere else," White says in a slight English accent. "I see this as a reward for my whole life as an archaeologist.“

Cologne's history cannot be told without taking a deep breath, for it begins with Agrippa, the commander of the Emperor Augustus and friend of the biblical King Herod, who in 19 BC resettled the Roman-friendly Ubian people on the left bank of the Rhine, roughly exactly where Gary White now stands. In the course of its 2000-year history, Germany's westernmost metropolis has been repeatedly demolished or destroyed and then rebuilt. So it happens that every Cologne stands on an older Cologne. Anyone who wants to learn about its earlier incarnations must therefore search underground.

After the Second World War, the ruins of the Praetorium, the governor's palace, suddenly rose out of the bomb craters. It is now being integrated into the museum that is being built. A few days ago, the breakthrough was made to the Jewish quarter from the Middle Ages, which was only rediscovered this century. Roman and medieval walls are built criss-cross over and through each other down here. The medieval Cologne people went for sustainability, so to speak, by reusing the old buildings as much as possible - they didn't have their own quarries.

Keep your head down! Now, under the guidance of site manager Matthias Zoppelt, we continue through a narrow corridor. On the right, two archaeologists are working in the light of a spotlight, behind them a larger room with a wonderfully preserved Roman archway opens up. In the Middle Ages, an inn was built here. This was already part of the Jewish quarter.

The Jewish community of Cologne - the oldest north of the Alps - was not a ghetto, but a city within the city, as it were, a miniature world of houses crowded together. It had a synagogue, a cult bath - the mikveh - a dance hall, a bakery, a bathhouse. All this is now suddenly back, only underground and in ruins. But you can actually walk through the houses again: "There in front was the Haus zum Golde, then comes Haus Nichols, Haus Koppe, Haus Bardowick and finally Haus Nussia," lists archaeologist Michael Wiehen. It is as if he were naming his neighbours.

A few steps further on, the medieval expert points to a sign with a Hebrew inscription. "A truly unique find," he enthuses. "We are here in the Lyvermann house." Lyvermann was a Jew from Düren who had his house here in the 13th century. This also included a latrine, a toilet. Here, however, there was a problem.

"Above the latrine is the courtyard that runs around the synagogue," Wiehen explains. "This area is sacred and must not be polluted. Latrines were normally cleaned from above, but this would have allowed faeces to enter the synagogue courtyard. That was not allowed. Mr Lyvermann therefore found a very clever special way." Instead of emptying from above, the latrine was emptied through the cellar. To make this clear to others, Lyvermann put up the sign with a kind of instruction manual. The inscription translates as "This is the window through which the excrement is taken out." This is probably as close as you can get to the Middle Ages.

In all, archaeologists have unearthed several hundred thousand objects, including a crescent-shaped, gem-studded gold earring from the 11th century and a plaque with the inscription "yt in ys neyt anders". This could be translated as: "Et is wie et is" (It is what it is). (It is how it is) - the classic Cologne saying. Finds like this show that for centuries the Jews were simply Cologne residents among Cologne residents.

But there are also the other finds. Michael Wiehen shows some inconspicuous black-grey chunks - they are the fragments of an iron chainmail that melted in a fire. "That means temperatures of over 1100 degrees." They were created on the night of 24 August 1349, when Jewish life in Cologne, then the largest city on German soil, came to an abrupt end.

In that year, the plague had come over the Alps and slowly crept towards Cologne from the south. With it, the rumour spread that the Jews had caused the plague by poisoning the wells. On the fatal night, the mob stormed over the wall that delimited the living space of the Jews, burned down the houses, slew men, women and children. "Pogrom debris" is what Gary White calls the remains of that night of murder. "This is the most important find of all.“

It includes written slates from the synagogue school, shopping lists, pictures, graffiti.... One particularly moving relic is kept in a box. It is only very small. A delicate flower carved from stone, once part of the synagogue's richly decorated reading pulpit, smashed into thousands of pieces that night. "It is very reminiscent of the architecture in Cologne Cathedral," says Michael Wiehen. The researchers therefore assume that the flower was created by one of the Christian stonemasons of the cathedral's construction lodge. Which shows how close the cooperation was. And how fragile.

(Original text: Christoph Driessen (dpa); Translation: Mareike Graepel)