The name may say it outright. Borremose translates as 'Borre'-bog, and Borre is plausibly derived from the old word burgh, a fortified place — a memory of function carried in a place-name long after the place stopped functioning. What the 1929 rediscovery exposed was a settlement built in the fourth century BC on a gravel bank measuring 140 by 90 metres, ringed by a moat 450 metres long, four metres wide and a metre and a half deep with a flat bottom, with earth mounds thrown up on the inner side. A cobbled causeway 150 metres long was the only way in from dry land. Inside stood ordinary longhouses — up to about twenty at any one time — but without byres, which is odd for an Iron Age farming community. Then, in the second century BC, the houses were burned and the whole site levelled to the ground.

The man found in May 1946 had a rope thirty-six centimetres long knotted around his neck with a slipknot when he came out of the peat. He was wearing two sheepskin capes and a woven cap, and examination found injuries to his skull and femur. Radiocarbon places him, and the other two, somewhere between 483 and 95 BC — the Pre-Roman Iron Age, contemporary with the fortress on the gravel bank rather than with the Bronze Age. The body found in 1947, about a kilometre away, was badly preserved; it was first identified as male, though that has since been questioned. With it lay a woman's skirt and a fringed shawl, one garment showing signs of earlier use as a man's cape, and two bones from a newborn infant. The 1948 find was a woman between twenty and thirty-five, lying face down under a large woollen skirt.

The rope is the hardest evidence, and it is hard to read as anything but a killing. Beyond that, honesty requires restraint. The Borremose woman's skull was extensively damaged, and forensic examination later found no evidence that the damage happened while she was alive — peat is heavy, and machinery is heavier. The infant bones beside the 1947 body are a fact without a story attached. What the bog preserves best are the ordinary things: a cap someone wove, a cape worn until it was reassigned to a different person, a skirt laid over a body. These were members of a farming community in Himmerland who died violently or were placed in water after dying, and the difference between those two sentences is the whole of the argument. They are not artefacts. They are the reason the artefacts are interesting.

Borremose was once far larger than the fragment that survives, and two neighbouring bogs were part of the same wetland. On 28 May 1891, peat cutters in Rævemose, less than a kilometre north near the hamlet of Gundestrup, lifted out a silver vessel that had been taken completely apart and stacked — five long plates, seven short ones, a base plate, and two lengths of tubing. Reassembled, the Gundestrup cauldron stands 42 centimetres high and 69 across, weighs just under nine kilograms, and is gilded, soldered with tin, and set with glass eyes. It is one of the most argued-over objects in European prehistory, dated variously between about 150 BC and the early Roman Iron Age, and it now sits in the National Museum of Denmark in Copenhagen. In 1875 a bronze kettle made by Etruscans around 300 BC came out of the nearby bog of Mosbæk. Whatever people were doing at Borremose, they were doing it with things from very far away.

The bog has not been kind to itself since. Industrial turf cutting during and after the Second World War hollowed out large sections, and the pits filled: much of Borremose is open water now. The northern part has grown over so densely with trees and scrub that it is impassable in most places, which is precisely why archaeologists expect it still holds finds. What can be visited is the fortress. After excavation, the outlines of the house sites were marked out with turf walls, the moats emptied and the ramparts rebuilt, so the whole settlement plan is legible on the ground. For a long time it was the only Iron Age fortified settlement known in Scandinavia — until a comparable site turned up at Lyngsmose near Ringkøbing in 1999. The type is now called a Borremose-fortification wherever it is found. Finds from the site are shown at the Museum Centre in nearby Aars, and a few kilometres southeast the Iron Age village of Østerbølle, with nine longhouses, has been restored.