British Archaeology #131 (July/August) has a feature by Pippa Bradley that caught my interest. It's about a Wessex Archaeology dig in 2004-05 at Cliffs End farm in Thanet, a piece of north-east Kent that was an island up until the 16th century when silting finished connecting it to mainland England. What we're dealing with here is ritual murder, some pretty strange disposal of the dead and ancient Scandinavian migrants.

Use of the site begins in earnest with six ring-ditch barrows during the Early Bronze Age (2200-1500 cal BC). These were poorly preserved and yielded few interesting finds. People then leave the barrows in peace for several centuries and don't return to the site in any serious way until the Late Bronze Age shortly before 1000 cal BC. And that's when the weirdness starts. Three round enclosure ditches are dug and re-dug, slighting five of the barrows. The ditches were found to contain household refuse, episodic feast remains and a burial or skull deposit (all shared with various pits inside the enclosures). And the smallest barrow gets slighted from another side by a continuous complex of at least 36 pits, some of them bearing evidence for re-cutting and re-use. The uncovered part measured 29 by more than 52 m. Here's where the weirdness turns to horrors.

Respectful Late Bronze Age burial in England is typically urned cremation in closely clustered cemeteries. The treatment of the bodies deposited in the Cliffs End pit complex is strikingly deviant. Basically what they're doing here is killing people and livestock, manipulating their remains ritually, often exposing them on site for a time, and finally inhuming them in pits. Bone preservation is perfect, leaving it all too clear what is going on. And it goes on for 800 years, well into the Middle Iron Age about 200 cal BC. A three-century hiatus during the Early Iron Age, I speculate, may be covered by the part of the feature that hasn't been excavated.

At least 24 people end up in sacrificial pits between 1000 and 800: males and females, ages 6 to 55. One large pit sees the following sequence (image above):

1. Redeposited human bones and two new-born lambs

2. Woman over 50, killed by sword blows to the back of the head

3. Another pair of lambs

4. Cow's head, two children and a teenage girl

5. Cattle foot and bag containing dismembered man, 30-35

6. More redeposited bones from people who died before the pit was dug (see below)

Some of the disarticulated bones from this pit are partly charred or gnawed by scavengers or show a patination typical of temporary deposition in a nearby midden. The excavators apparently interpret the animal parts and certain small artefacts in the pit as grave goods, but to my mind nothing in the pit should be seen as a respectful burial: human bodies, livestock and artefacts are all sacrificial gifts to some particularly blood-thirsty deity. The artefact finds are mainly pottery, but also a rare and interesting lead weight and part of a bone balance. Weights and balances are indicative of trade and a grasp of mathematics, but are also important tools when composing metal alloys such as the period's all-important bronze. Scandinavian weights of the same era take the shape of little female statuettes wearing paired torque neck rings, and we find the paired torques as wetland sacrifices.

Iron Age practices in the sacrificial pit complex are less intense and intricate: over a period of three centuries, eight people get buried whole and seven disarticulated bone bundles are deposited. One young man is buried on top of half a horse. The bone bundles bear signs of scavenging by dogs.

Who were these people then? Could anybody at Cliffs End get roped in for sacrifice and be denied respectful burial at the whim of the local druid? Historical and ethnographic accounts suggest that this is unlikely. Small low-tech societies have a strong sense of in-group versus out-group. If you don't get your urn in the clan's urn field in this era, it's highly likely that you are simply not a clan member. And here's where stable isotopes come in, a fantastic data source that sees more and more use in interpreting bone finds. Among the questions isotopes can answer today are main food sources and geographical area of residence.

Andrew Millard of Durham University analysed all suitable teeth from 25 individuals. Here's the geographical breakdown of the sacrificial victims' area of origin:

36% local

32% southern Norway or Sweden

20% western Mediterranean

12% indeterminate

The reason that you do more than one tooth from the same individual is that teeth form in sequence during gestation, childhood and adolescence. If you move or change your diet during that period, this shows up in the isotope ratios of whatever tooth your body is making at the time. This gave particularly interesting results in the case of an old woman whose disarticulated skull was redeposited in the Late Bronze Age charnel pit discussed above. She was born in Scandinavia, moved to northern Britain as a child, lived a long life and finally ended up as a prop in a religious ritual on Thanet.

More than half of the victims are foreigners. And though more than a third are locals, we don't know if their parents were locals as DNA hasn't been done yet. Who travels like this in the 1st millennium BC? Certainly not tourists. Traders do travel, but for a community dependent on long-distance bronze deliveries, it would not be a sustainable strategy to ambush and kill the traders – never mind that these were in all likelihood well organised and armed. My guess is that we're dealing with slave raiding and slave trade. Goods travelled, and one valuable commodity was slaves. All valuable commodities were appropriate as sacrifices to the gods when that time came.

In the case of the well-travelled old woman, I imagine her being taken from her tribe in southern Norway by Scottish slave raiders, growing up in Scotland, and then being traded on maturity to a Kentish tribe with odd religious practices. She probably gives birth to more slaves there (perhaps a few of the recovered individuals with local isotope signatures) and lives most of her adult life at Cliffs End. Not as a member of the clan, but as property of a clan member. And then comes that final Beltane feast out by the barrows.

Check out Wessex Archaeology's on-line exhibition on Cliffs End! A monograph is in press: Jacqueline McKinley et al., Cliffs End Farm, Isle of Thanet, Kent: a mortuary & ritual site of the Bronze Age, Iron Age and Anglo-Saxon Period with evidence for long-distance maritime mobility.