Offa's Dyke may not be made by Offa
It's called Offa's Dyke - but today experts came up with the startling revelation that it may have nothing to do with King Offa.
The historic earthwork, which runs through parts of Shropshire and Mid Wales, has always been associated with the king, who ruled the kingdom of Mercia in the second half of the eighth century.
But archaeologists from the Clwyd-Powys Archaeological Trust have uncovered evidence thath suggests that the structure may have been built up to 200 years before the reign of King Offa.
Samples from the trust's excavations on a stretch of the dyke near Chirk have been radiocarbon dated to the second half of the sixth century.
The dated material came from an ancient layer of redeposited turf underneath the bank, suggesting that this material was laid down as part of the construction process.
The archaeologists' work is the first time that accurate scientific dates have been obtained from Offa's Dyke.
Expert Paul Belford said: "This is tremendously exciting. We must re-think some of our assumptions about this important monument.
"Certainly the dyke was built to make a statement about the power of the kingdom of Mercia.
"However it is now clear that it was not the work of a single ruler but a longer-term project that began at an earlier stage in the development of the kingdom."
The experts say the dyke is a "physical manifestation" of the increasing political centralisation that was taking place across Europe in the post-Roman period, and which eventually led to the emergence of the nation states that exist today.
The modern border between England and Wales closely follows much of the route of the Dyke.
Mr Bedford added: "Of course these samples are from only one section of the dyke. Further work is needed on other parts of this enigmatic monument before we can really say who built it and why."
Offa's Dyke is the longest linear earthwork in the UK, and one of the longest in Europe.
Fieldwork on the Offa's Dyke project was started in August last year in response to an unauthorised removal of part of the Scheduled Ancient Monument near Chirk.
The Clwyd-Powys Archaeological Trust is one of four Welsh Archaeological Trusts working to help protect, record and interpret all aspects of the historic environment.