As my train from Hamburg to Denmark chugged past soggy green fields and sun-dappled birch forests, we passed yet another willow-shrouded bog topped with blue green algae or tidy duckweed. Even from the moving train, I could sense they were dark and gentle places, peaceful waterholes like the one I imagine Hamlet’s ill-fated lover Ophelia drowned in near Elsinore. My train had entered bog body country.

Bog bodies are 2,000-year old humans discovered in the bogs, mires and moors across Northern Europe, from Ireland to Poland.

Many modern archeologists believe that these Iron Age people were sacrificial victims, killed and then delicately deposited in the bog as a ritualistic offering to the gods. Other scholars speculate that they were criminals, immigrants or wayfarers.

Denmark has one of the world’s highest concentrations of bogs and bog bodies – many perfectly preserved over the centuries, pickle-like, by acids generated by sphagnum moss, the living foundations of these wetlands. Most were accidently discovered by turf harvesters between 1800 and 1960 when Denmark still burned peat as fuel.

Forensics and modern autopsies have revealed that almost all of them – both men and women – met a violent end, some with finely wrought nooses around their necks and others with horrifically slashed necks.

Because very little is known about Iron Age Denmark – there was no written language in Denmark then, and few written texts of Romans and Greeks survive – we can only speculate as to who they were and why they were murdered. However, since the majority of Iron Age people were cremated, we do know that these souls met a distinctly different end from their contemporaries. I wanted to visit these bog bodies to get a better insight into the mysterious world they came from.

My first stop was Vejle, a small city of about 100,000 in southeast Jutland, 240km west of Copenhagen. The gorgeous, hilly region is atypical of flat Denmark. The roads corkscrewed around gently rolling farm hills and undulating glacially sculpted valleys, pocked with kettle ponds and woodsy bogs lined with pink orchids and stiff umber cattails.

I was there to meet with Mads Ravn, head archeologist at the Vejle Museum, who oversees a fascinating collection of artefacts, including Roman coins, inscribed swords and swastika brooches (an ancient symbol that existed before its association with the Nazi Party) that were all found in the bogs and are thought to be votive offerings, possibly for Iron Age gods or deities.

From a dark room in the back of the museum, I heard the gloomy call of the elk antler horn, piped in here by modern speakers, but often used as a distress call in Iron Age Denmark. I heeded its call and entered. In the darkness lay the thin leathery body of Haraldskær Woman in an open glass sarcophagus, the expression on her ashy face fixed in a state of shock. She was not as peaceful as bog bodies I’d seen in books; it was eerie and I felt like I was intruding on her privacy.

“When she was discovered by peat diggers in 1835, she was thought to be the 10th-century Viking Queen Gunhildd, who according to the Jomsvikinga Saga was drowned by her husband Harald Bluetooth” said Ravn, scratching his beard and looking at her puzzlingly.

“But that’s untrue and we now know from radiocarbon dating that she’s about 2,200 years old.”

Haraldskær Woman was found naked aside her cloak and was pinned down in the bog by tree branches, probably after she died. Grooves on her neck suggest strangulation. Additional forensic analysis revealed her stomach contents at the time of her death, which included unhusked millet and blackberries, a strange last meal for a meat-centric society.

“We’re now doing isotope analysis on her hair and working with a new DNA technique that’s extracting DNA from the inner ear. We’re hoping to get results soon so we can find out more about her.”

Ravn and I drove 10km west to the unmarked Haraldskær (Harald’s Bog), where Haraldskær Woman was discovered. Like the bogs I’d seen from the train, it was covered in bright green duckweed and surrounded by a dense thicket of trees, under which crooked purple mushrooms and bright red berries burst with color in pockets of sunlight. There’s something magical and otherworldly about these bogs, and it’s easy to see why they were once chosen as sacrificial sites – and why they maintain an inexplicable magnetic pull today.

My next stop was Aarhus, Denmark’s second biggest city, to visit the breathtaking new Moesgaard Museum that’s home to one of the best exhibits on Iron Age Europe. The star attraction here is Grauballe Man. Discovered in 1952, the perfectly preserved bog body sits in a natural, almost yoga-like, lounging position, his feet and skin almost entirely intact, his face elegant with sharp features and a button nose.

“Like most bog bodies, his hair and skin was turned red by a chemical process called the Maillard reaction,” Pauline Asingh, archeologist and head of exhibitions, explained. “He’s really a beautiful man,” she said

But the serene look on Grauballe Man’s face belies his violent ending. “He was forced on his knees and his throat was slashed from ear to ear by someone standing behind him. But he was deposited with care into the bog,” Asingh continued. “It might sound violent and careless to us, but sacrifices were an important part of cultural life in this period.”

Asingh led me to another exhibit, this time on bog dogs. In 2015, 13 sacrificed dogs from around 250AD were found in the Skødstrup bog near Aarhus, suggesting that ritualistic sacrifice wasn’t limited to humans. In fact, the exhibit included a series of emotional animated shorts that captured the spirit of devotion behind these often violent sacrifices. In one, a young girl puts a wreath of flowers around her dog’s neck before it’s killed. My visit to Moesgaard reminded me that although it can be tempting to simplify the past, these are people, not artefacts, each with their own complicated life story.

My final stop was to the small town of Silkeborg, 44km west of Aarhus. Here, the butter-yellow Museum Silkeborg has a small but powerful display on bog bodies and is home to one of the best preserved specimens in the world. Tollund Man, about 2,400 years old, is so remarkably undamaged that when his body was discovered in the 1950s, authorities thought it might be a boy who’d been reported missing.

Like some of his fellow bog bodies, he was hanged; the intricately woven noose that killed him was still around his neck, but his long nose and smooth brow were perfectly intact, his full lips curled in a mysterious semi-smile.

In the next room was Elling Woman, who was found just 40m from Tollund Man and is thought to have died around the same time. She’s also believed to have been hanged, and is beloved for her fabulous hair, a 90cm red braid tied in an elaborate knot.

Ole Nielsen, the museum archaeologist, drove me to the Bjældskovdal, a sprawling raised bog about 15km away where the two bodies were found. It’s since been preserved as a nature park and is lined with wooden boardwalks and signed trails. During our brisk walk, a light mist hovered over the lake-like bog, and we spied great blue herons, mallard ducks, violet flowers and of course spongy sphagnum moss.

As we stopped to regard the bog, I wondered what other secrets its murky depths were hiding. The bog flowed slowly and hungrily, preserving everything that fell into it for millennia, a reminder of its everlasting and awesome power.

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