The Yorkshire war had tilted Royalist that winter. In December 1642 the Earl of Newcastle had marched south from his namesake city and taken York, Tadcaster and Leeds in succession. Then in late January 1643 the Parliamentarians retook Leeds, and the two armies settled in to watch each other through the rest of the cold months. By spring Lord Ferdinando Fairfax wanted to move his field army from Selby up to Leeds, but his slow artillery train was vulnerable on the road. He told his son Thomas to ride east, threaten Tadcaster, and pull the Royalists' attention north. The plan worked - briefly. The Royalist garrison at Tadcaster ran rather than fight. Thomas spent a few hours pulling down their works, then set off west to rejoin his father. He did not know that Newcastle had already sent George Goring with twenty troops of horse to find him.

The infantry Thomas Fairfax commanded that day were not professional soldiers. They were Yorkshire countrymen - clothiers, farmers, apprentices from the wool towns - and they had been on their feet for hours. At Bramham Moor they had halted of their own accord, waiting for orders they did not need. Once across they thought they were safe and broke ranks at a village to look for ale. Fairfax and his officers chased them back into formation each time. None of this is the stuff of legend. It is the stuff of real war, the friction that gets men killed. Goring shadowed them all the while, looking for the moment when the column would string itself out on a stretch of open ground.

It came at Whinmoor. The Royalist cavalry swung wide around the enclosed fields north of the road, found their way onto the moor undetected, and struck the Parliamentarian foot from rear and flank simultaneously. Fairfax's men had no pikemen worth the name - musketeers without pikes are defenceless when the powder runs out and the horses come on. The line dissolved in minutes. The countrymen threw down their weapons. Many were ridden down where they stood. More were taken prisoner. Some simply walked away, found a hedge, kept their heads down and made their way home over the next few days. Fairfax and what remained of his cavalry broke out to the west and rode hard for Leeds.

Lord Fairfax got his guns to Leeds. The diversion had technically worked. But when news of the moor reached the wool towns, the families of the missing men came for Thomas Fairfax. The criticism was so severe that he resolved to make it right by force. On 21 May he led a sudden assault on the Royalist garrison at Wakefield, capturing more prisoners than he had men under his own command - prisoners he could trade for the ones lost on Whinmoor. It was an extraordinary recovery and the start of Fairfax's reputation as one of the most aggressive field commanders of the war. He would, within four years, lead the New Model Army to victory at Naseby. The lesson of Seacroft Moor had stuck.

There is no battlefield to walk today. Whinmoor is a Leeds suburb. The A64 York Road cuts through what was once open heather; semis and small parades of shops have replaced the moor. A single information board near Seacroft Ring Road marks the action. The site is more visible from the air than the ground - a low ridge running east-west, gently falling toward the old village of Seacroft, with the city of Leeds rising to the west. Knowing what happened here changes how you see it: a thousand men taken prisoner along a stretch of road now busy with school buses and delivery vans.