High-speed rail may have met its most formidable opponent yet – the ghosts of a Welsh army slaughtered fighting for an English king more than 500 years ago.
As many as 5,000 soldiers from Wales, including more than 180 knights and noblemen, lie buried somewhere in farmland north of Banbury, Oxfordshire. In the centuries after they were cut down, at the battle of Edgcote in 1469, one of the bloodiest clashes of the Wars of the Roses, the precise location was forgotten.
But historians and heritage campaigners fear that the proposed HS2 line could pierce its heart and, potentially, plough through mass graves.
Uncertainty about the position of the battle site calls into question assurances offered by High Speed Two, the company set up to oversee the £35bn scheme, that the line avoids the battlefield. It is not a protected site, and has never been investigated by archaeologists.
English Heritage, the government agency, has revealed to the Observer that "a large number" of unprotected historic sites and buildings, all along the proposed HS2 route, have yet to be assessed by High Speed Two – a key requirement of the formal environmental impact statement which must be completed, in detail, by the company.
The first phase of the HS2 scheme, London to Birmingham, passes through or alongside several historically sensitive sites. Dozens of ancient buildings, listed and unlisted, are also at risk. Last month the line's second phase was announced, with routes north from Birmingham to Manchester and Leeds.
The battle of Edgcote, fought in July 1469, pitted Welsh forces under the Earl of Pembroke against rebels from the north of England trying to depose the Yorkist king, Edward IV, in favour of the Earl of Warwick, the "Kingmaker".
A ferocious struggle involving as many as 40,000 troops, the battle claimed the lives of the flower of Welsh society. It was the largest loss of Welsh troops on a single day until the first world war, and has been dubbed "the Welsh Flodden" – the battle of 1513 in which England crushed Scottish military power and its ruling elite.
"Edgcote is an extremely important site for Welsh culture and traditions, but its study is very neglected," said Dr Barry Lewis, of the Centre for Advanced Welsh and Celtic Studies, Aberystwyth. "Edgcote was remembered for 100 years afterwards. Welsh people were still talking about revenge for the battle. We don't want development going through any battlefields."
The loss of life was especially bitter for Wales as its forces were apparently left undefended by English archers, following a row on the eve of battle between the archers' commander, the Earl of Devon, and Pembroke. Some chroniclers blame this fatal falling-out on a dispute over lodgings, but one suggests they locked horns over an inn-keeper's daughter.
Lewis has studied the work of Welsh poets, writing in the aftermath of the disaster. They record betrayal by the English at the battle they call Banbury.
One poet, Lewys Glyn Cothi, mourns: "The mightiest [battle] of Christendom,/ And through a fault it was lost:/ At Banbury the vengeance was exacted/ Upon fair Wales, and the great fine.
"There was heard all at once/ Crying of battle between great spears."
Another poet, Guto'r Glyn, records simply: "I was killed, I and my nation too."
Edgcote battlefield is not included on English Heritage's Battlefields Register, a list that could help boost protection. The agency is considering an application to place it on the list. A spokesperson told the Observer: "The Edgcote battlefield is one of a possibly large number of undesignated heritage sites that HS2 has yet to work on to establish whether or not there is an impact, and if so how it might be mitigated.
"Our advice to HS2 has been that they do need to have done this to inform their environmental impact statement."
High Speed Two denies that the battlefield will be damaged by the rail scheme. It says that the route has been amended to take account of historically sensitive sites. A spokesman told the Observer: "Changes included moving the route away from a cluster of important heritage sites around Edgcote. This realignment farther away from Edgcote House and its grounds avoids the site of a Roman villa and the possible location of the historic Edgcote Moor battlefield."
Campaigners are highly sceptical about High Speed Two's assurances, and say that mention of the battlefield was omitted altogether from initial drafts of the HS2 route.
"We are well aware of the general area of the battlefield, but nobody can be 100% sure until it has been properly surveyed. Anyone who claims the contrary is talking nonsense," said Harvey Watson, of the Battlefields Trust. "We are hoping that an amendment to the route in 2012 will mitigate the worst impact of this, but until a detailed survey has been carried out we cannot be sure."