ON a warm September day almost 1,000 years ago, a line of English soldiers crouched behind a wall of shields in the marshes beside the River Ouse at what is now Fulford Ings. Ranged against them were the 7,000 or so Viking troops of the Norwegian king, Harald Hardraada.

It was September 20, 1066 - and the battle that was about to take place, says Keith Mulhearn, was to play its part in shaping the future of England for a thousand years to come.

For the English soldiers, mustered under the twin banners of Morcar, Earl of Northumbria (of which York was capital) and his brother Edwin, Earl of Mercia, the Vikings must have been a terrifying sight.

Keith's new book - Fulford: The First Battle of 1066 - provides a vivid description.

On Hardraada's signal, he writes, the Vikings moved forward, all banging their swords and axes on their round, lime-wood shields. "It was common for soldiers of this time, especially Vikings, to take drugs before battle, usually mushrooms to work themselves into a frenzy," Keith writes.

"These men were called 'berserkers' and there is no doubt that they were at the front line that day, screaming and shouting like men possessed and not really caring whether they lived or died."

At first the 5,000 or so English troops held firm, and even began to push the Vikings back. But then the Viking left flank rallied and, led by Tostig, the renegade brother of England's King Harold Godwinson, cut behind Morcar's elite household guards or housecarls and trapped the English in a pincer movement.

One group of English soldiers under Edwin fled along the Ouse. The rest were cut down as they tried to scramble across what is now Germany Beck or were speared as they tried to swim across the Ouse.

The Housecarls, Keith writes, were surrounded by the Vikings and cut to pieces. "Many drowned in the marshes, too weak to raise their heads from the water because of their wounds. It is said there were so many bodies lying dead in the marshes that the Vikings could walk across without getting their feet wet."

So ended the first of three great battles of 1066 that were to shape the future of England for the next Millennium. That year, says Keith - a tour guide who runs Roam'in Tours in York - was a year of enormous upheavals. "It is hard to believe that so many events and coincidences occurred in just 12 months," he writes. "We saw two kings die and two crowned. There were three major battles, one of which was won after a 200 mile march, another lost because of one."

It all began with the death of King Edward the Confessor on January 5. Three men felt they had a claim to the English throne: Harold Godwinson, the Earl of Wessex; William, Duke of Normandy; and Harald Hardraada, King of Norway.

Possession is nine tenths of the law. Harold was in England, and had himself crowned King the day after Edward's death. The storm clouds were gathering.

His renegade brother Tostig linked up with Hardraada and his Vikings for an invasion of the north, while Duke William threatened an invasion across the English channel to the south.

King Harold initially decided to allow the northern earls Morcar and Edwin to deal with Hardraada and his Vikings, while he waited for William.

Hardraada's fleet, after landing at Scarborough on September 12, sailed up the Humber and then the Ouse to Riccall. A messenger despatched to alert King Harold reached him some time on Tuesday September 19. With bad weather delaying William's crossing, the King decided to march 200 miles north with his army.

He arrived too late to influence the outcome of the Battle of Fulford, Keith writes. But five days later he caught up with Hardraada's army at Stamford Bridge.

It was a hot day. The Vikings, not thinking King Harold could have travelled so far so fast, were not expecting a battle, Keith says. They had gone to Stamford Bridge to receive a delegation from York, who were to hand over 100 hostages and recognise Hardraada as King. Because of the heat they had left their armour plus a third of their army behind at Riccall.

King Harold defeated the Viking king - after famously, before the battle, offering him 'seven feet of English ground' - and promptly set out with his weary army on the forced march 200 miles back down to Hastings, and the fatal confrontation with Duke William.

But Keith likes to speculate on what might have happened if the outcome of the first two battles, at Fulford and Stamford Bridge, had been different.

If the English had won at Fulford, he believes, a messenger could have been despatched to King Harold so that he and his army would not have needed to march all the way up to York. They could have been fresh and ready, waiting for William of Normandy to land - and the outcome of the Battle of Hastings might have been different. "So if they had won at Fulford, it could have significantly changed the course of English history."

On the other hand, if the English under King Harold, weary from their 200 mile march northwards, had lost to the Vikings at Stamford Bridge, history would again have been different.

Hardraada and William of Normandy, he believes, being both of Norse descent, would not have fought each-other. "So if Hardraada had won, he might perhaps have kept the north, and William the south. There could have been a north/south divide."

What really surprises him, says the 36-year-old father of three, is how little has been written about the Battle of Fulford. He himself made a slight reference to the battle in a York guide book he wrote a few years ago: but there was very little else.

When writing Fulford, The First Battle of 1066, he relied heavily on ancient texts - the Anglo-Saxon Chronicles and the Icelandic saga of Snorri Sturlasson - as well as making use of his knowledge of the terrain and of the fighting methods of the time.

The result is a short but highly readable booklet, that includes a map and three 'battlefield trails' so that you can see the site of the great battle for yourself.

As Keith writes, no one can be completely sure of the exact train of events that day - only of the outcome. But we have been living with the consequences for a thousand years.

- Fulford: The First Battle of 1066 by Keith Mulhearn is published by Roam'in Tours and is available from York Tourist Information Centre, Barley Hall and the Monk Bar and Micklegate Bar museums, priced £4.50.

Updated: 10:10 Monday, September 30, 2002