The early years of the 400s were one of turmoil in Western Europe, as the Roman Empire lurched from crisis to crisis. While there is no specific date for the end of Roman rule in Britain, it was over by at least 410CE. 

At this time, the genetic makeup of England was primarily comprised of Celtic ancestry, with significant contributions from continental Europeans as a result of the Romans. The genetics of Wales and Scotland, meanwhile, remained more distinctly Celtic.

Over the next few hundred years, the arrival of Europeans contributed to the formation of Anglo-Saxon culture in England, which would dominate until the arrival of the Normans in 1066. However, whether this migration was peaceful, or ensured by force, has been debated for many years.

A lack of widespread archaeological evidence had been used by historians to suggest that England was ruled by a small but elite group of Anglo-Saxons which led to the adoption of their culture over time. However, this theory did not explain why in some areas these individuals can be found buried side by side with Britons.

More recently, advances in extracting DNA from ancient skeletons have allowed researchers to sequence the genomes of the long dead, allowing them to infer changes in the population over time. 

Dr Selina Brace, a Museum specialist in aDNA and another of the paper's co-authors, explains the process.

'When attempting to extract DNA from bone, we would typically begin by drilling a small hole into it using a drill similar to the kind a dentist might use,' Selina explains. 'This is so that we can drill at a slow speed without generating too much heat that might damage the DNA further.'

'We remove a small amount of bone powder, using chemicals to break down the bone and extract the DNA. Finally, we prepare the DNA for sequencing using a process called library building.'

Previous studies have suggested that the mixing of continental Europeans and Britons provided the basis of Anglo-Saxon ancestry in Britain, along with arrivals from further afield. However, these studies only looked at DNA from a handful of individuals.

By increasing the scope of these investigations to almost 500 human remains, including 285 from England, the new paper provides the most detailed insight yet into the development of the Anglo-Saxon people.

'Earlier, prehistoric time periods have previously been worked on at a similar scale to this study, but they are more straightforward to investigate because population transitions are taking places between groups which are completely different to each other,' Ian explains. 'This means they can be identified more easily.'

'The demographic changes we see in the Anglo-Saxon migration are between groups that are comparatively closely related to each other, so you need more sophisticated techniques to identify them.'