A new technique lets archaeologists reconstruct the past in greater detail

THAT economic expansion leads to building booms seems to have been as true 6,000 years ago as it is now. When agriculture came to Britain, it led to a surge of construction as impressive—and rapid—as the one that followed the industrial revolution.

Which is all a bit of a surprise to archaeologists, who had previously seen the arrival of the Neolithic as a rather gentle thing. But that may be because of the tools they use. Radiocarbon dating provides a range, often spanning 200 years or more, rather than an exact date for a site. Stratigraphy, which looks at the soil layers in which artefacts are found, tells you only which ones are older and which younger. None of these data is precise. They do, however, limit the possible range of dates. And by using a statistical technique called Bayesian analysis it is possible to combine such disparate pieces of information to produce a consolidated estimate that is more accurate than any of its components. That results in a range that spans decades, not centuries.

A team led by Alex Bayliss, from English Heritage, a British government agency, has just used this technique to examine digs from hundreds of sites around Britain. The results have caused them to reinterpret the Neolithic past quite radically.

Agriculture seems to have arrived fully formed in what is now Kent, in the south-east, around 4050BC. The new culture spread slowly at first, taking 200 years to reach modern-day Cheltenham, in the west, but over the following five decades it penetrated as far north as Aberdeen. Soon afterwards, causewayed enclosures (circular arrangements of banks and ditches hundreds of metres across—see picture) began springing up all over the country.

Until now, archaeologists had assumed that these were built over the course of centuries. Dr Bayliss’s work suggests they were the product of two booms, each just a few decades long—for the Neolithic seems to have seen its share of busts, too.

The team’s work offers such a sharp picture of the past that it is possible to trace the histories even of individual communities, such as one in Essex whose inhabitants built, used and then abandoned an enclosure within the span of a single generation.

English Heritage now plans to apply the technique to another murky era of British history, the early Anglo-Saxon period between 400AD and 700AD. In principle, the method can be applied to any archaeological site, and several groups of researchers around the world are working on similar projects. But, fittingly for a discipline that deals in centuries and millennia, the revolution will be a slow one. Unlike traditional radiocarbon dating, which can be bought off the shelf, Dr Bayliss reckons it takes between three and four years to train a graduate researcher to use the new technique properly.

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