Hans-Ole Hansen was a teenager when he watched a film about Stone Age people and decided the thing to do was make a flint axe himself, with bone and wood and stone, no modern tools involved. Curiosity of that kind does not usually turn into an institution. His did. In 1964 he founded the Historisk-arkæologisk Forsøgscenter with Svend Nielsen and Professor Axel Steensberg, and got backing where it counted: the Minister of Education, Jørgen Jørgensen, the National Antiquarian, P. V. Glob, and Viscount Knud Holstein-Ledreborg, who leased him the land for a hundred years. Hansen ran the centre from 1966 to 1985 and built or restored twenty-five houses in that time. Glob gave him one piece of advice that shaped everything after: you are not a scientist, but a teacher.

The reconstructions are grouped by period and given names. Lethra is the Iron Age village - four rebuilt farmsteads representing the centuries between 200 BC and AD 200, with a sacrificial bog to go with them. Athra is a Stone Age camp of the Ertebølle culture, that long Mesolithic stretch from about 5500 to 3900 BC. There is a Viking market place, and the Krikkebjerg cottages, Hørhavehuset and Tystruphuset, standing in for the smallholdings of the Danish nineteenth century. Livestock matter as much as buildings: some of the animals are breeds chosen to approximate the size and build of Iron Age stock, now extinct, and others are nineteenth-century Danish breeds. The workshops - the potter's, the weaver's, the smithy - are not display cases. They make the tools, clothes and household goods that the reconstructed settlements use.

Experimental archaeology works because it can be wrong. A roof that will not shed rain, a kiln that will not reach temperature, a grain store that rots - each of those failures narrows the range of what people in the past can plausibly have done. Lejre has run the full sweep: house construction, pottery firing, the detailed reconstruction of ancient food production, and the crafts that surround all of it. Archaeologists come from around the world to run experiments here on their own questions. Among the people Lejre supported was Errett Callahan, an American who died in 2019 and who was one of the most accomplished flintknappers anyone has produced - a man who could return a stone tool to the state of the hand that made it.

Each summer, families move in. They stay a week in the Iron Age village, in the farm cottages or at the Stone Age camp, wearing period clothing and taking on the work of the settlement they are living in - cooking on fire, tending animals, sleeping in smoke-darkened rooms with no switch to flick. It is participation rather than performance, and it draws on Glob's insight that a centre teaching people would outlive one merely researching them. Something around 55,000 to 60,000 visitors come through in a year, a large share of them schoolchildren. The gap between reading about a longhouse and waking up in one is the entire product.

Location was not an accident. One kilometre east lies Gammel Lejre, a place of real archaeological weight: a major political centre of Iron Age and Viking Scandinavia, the seat medieval legend gives to the Skjöldung kings, and the site long identified as the real counterpart of Heorot, King Hrothgar's hall in Beowulf. Excavations since the 1980s have found an extensive Iron Age and Viking settlement complex there. The experimental centre does not excavate that story, and it should not be confused with it. But there is something appropriate about testing how a longhouse is built, how long its roof lasts, and what it leaves behind when it burns, on the doorstep of the landscape where the most famous halls in northern legend were supposed to have stood.