Berlin’s history is visible on every corner:  museums, memorials, documentation centres, commemorative plaques and surviving sections of the Berlin Wall. None of these are needed for this history lesson. You only have to look down at your feet. A dozen people are doing just that outside the former royal officials’ residence at Geschwister-Scholl-Straße 5 in Mitte during Open Monument Day.

Standing in front of the group is a middle-aged man with an engaging smile, a khaki backpack and a large presentation folder in his hand. “Hans Greiner, 51, married, no children, two cats” – that is how he introduces himself at the start of his tour, “Wartime Damage on Berlin Pavements”. Then the engineer and software quality assurance specialist gets to the point: Why does the tour begin here of all places? The façade of the former royal officials’ residence was renovated in 2010 in such a way that the impact marks remained visible.

Searching for Clues with the “Stone Whisperer”

A veritable treasure trove for Greiner, who has been described as a tracker, pavement researcher or stone whisperer. For years, he has been studying the historic Prussian granite slabs used in Berlin since 1824. The heavy slabs are smooth on top and curved underneath. Hence their name: Schweinebäuche – “pig bellies”. The wartime traces may have been caused by small arms, explosive projectiles or incendiary bombs. Visible signs include impact marks, chips and so-called shrapnel roses – scratches caused by fragments around the centre of an explosion. Their shape, depth and direction provide clues, but rarely certainty.

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The tour continues to Weidendamm on the banks of the Spree. Hans Greiner stops beside a round depression in the pavement. Here, it finally becomes clear why someone with the city’s history at his fingertips needs to carry so much equipment on his tour. He pulls out a kiwi-green hand brush, kneels down and carefully sweeps out the crater – as if he were cleaning at home.

“I actually have half a pig belly in my living room too; my wife allows it,” he admits with a grin. Then he places a small grey hexagonal template into the depression. “I’ve only seen a more perfect crater of this kind in one other place. It brought tears to my eyes,” he admits. Wartime traces like these, found all over Berlin, had captured his fascination. He wanted to understand how they had been created.

Paving Stones Raise Questions

“The impacts probably came almost vertically from above. I just couldn’t explain why.” At first, the pavement researcher suspected that the pig bellies might have been propped upright during street fighting and used as cover. But he found no photographic evidence of this. Today, he considers British INC-4-LB incendiary bombs the more likely explanation: narrow, stick-like incendiary devices, tens of thousands of which were dropped over Berlin during night-time air raids.

At this point, Greiner conjures another demonstration piece from his backpack: a scale replica of an incendiary stick bomb. His father built it. A heavy metal rod, a good half-metre long and with a hexagonal cross-section, is passed from hand to hand. The 51-year-old explains how it worked – from its falling weight to its ignition mechanism – in a level of detail that only a few knowledgeable members of the group are able to follow.

90 Minutes of Stories About Pavements? “Cool”

On the way to the next site, it becomes clear why “the uninitiated”, such as Stefan Kroon, choose to join this tour. The 40-year-old actually came to Berlin from Wuppertal to visit friends and party. Nevertheless, history is part of every Berlin weekend for him. He has several stops planned for Open Monument Day: the Topography of Terror, the Federal Ministry of Finance – and Greiner’s pavements. “What is this guy going to tell me about paving stones for 90 minutes?” he wondered when he clicked the registration button. By now, he thinks it is pretty “cool” to know about things you would otherwise simply walk past.

Past the Bode Museum, the Alte Nationalgalerie and Berlin Cathedral, the tour moves from one site to the next. At the end of the tour, we drop onto a bench with Hans Greiner. A few details still need clearing up: which site was it again that had brought even a seasoned tracker like him to tears? “RUEIT01,” Greiner shoots back, without a second of hesitation.

I actually have half a pig belly in my living room too; my wife allows it.

Hans Greiner, Pavement researcher

He may not have a museum, but he certainly has its organisational system: every find is assigned its own code in the digital archive. “RUEIT01” stands for the almost perfectly hexagonal crater on Eitelstraße in Rummelsburg, Lichtenberg. The pavement researcher records his research hours just as meticulously. By now, he devotes three full working days a week to searching for traces.

How a Piece of Pavement Ended Up in His Living Room

One story is still missing, however: how did a piece of Berlin pavement end up in his living room? In spring, he happened to drive past Scharnhorststraße 34–35 by the Invalidenfriedhof cemetery, where the pavement was being renewed. He immediately got talking to the construction crew about his work. “Whatever floats your boat,” they said. The old slabs were going to be disposed of anyway. He could have one. But the chunk of granite was impossible to move on his own, so the construction crew had to help load it. Naturally, there was a crate of beer for them in return.

Today, the half pig belly stands on a pedestal against the living-room wall, professionally illuminated like a precious museum exhibit. In the photo the tour guide shows, his grey cat is crouching on the stone, almost blending into the granite. The only colourful things in the picture are the Easter eggs in the wartime craters.