The grisly discovery of 8000-year-old human skulls impaled on stakes in Sweden has left archaeologists puzzled.

In 2009, construction work on a railway bridge across the Motala Strom River, in the south of the country, unearthed artifacts such as animal bones, primitive tools and wooden stakes from thousands of years ago.

Two years later, a team of archaeologists from the Cultural Heritage Foundation began excavating the area at Kanaljorden.

This week the team’s findings were published in the journal Antiquity , under the title: ‘Keep your head high’.

Their discovery of human skulls on stakes was grisly enough, but it also shatters the conventional view of hunter gatherers.

Other digs from the Mesolithic period show the dead were respected, and it wasn’t until later years that tribes were known to have decapitated enemies.

The 10 skulls uncovered at Kanaljorden – belonging to nine adults and one child – did not have jaw bones and two had well-preserved wooden stakes lodged inside them.

The excavation site at Kanaljorden unearthed hundreds of artefacts. (Image: Twitter).

All the adult skulls showed blunt force trauma near the top of the heads. But they also had other cranium injuries that show signs of healing.

“These are not people who have been recently smashed in the head and then put on display," Fredrik Hallgren, of the Cultural Heritage Foundation, told National Geographic.

"More than half of them had this healed trauma to the head."

The archaeologists were unable to identity the weapon that made the wounds, but the injures seem to have occurred by violence rather than accidents.

There’s also evidence that suggests the bodies had been buried before the heads were dug out.