The Yorkists were led by the Earl of Warwick and the Earl of March, who had sailed from Calais in an attempt to remove King Henry VI from the influence of his Lancastrian advisors.
When Warwick and March arrived from France the Lancastrians left London, which was seen as having Yorkist sympathies, and marched to Northampton. They set up in the deer park of Delapre Abbey, which was bordered by a ditch and 10-foot high fence. This was to be the only time during the Wars of the Roses that an attack on a fortified camp was attempted.
The Lancastrian lines were further protected by a collection of canon. However, as the Yorkist army started its advance, a heavy rain shower soaked the charges and stopped the guns from firing.
The battle initially hung in the balance, with the Yorkist soldiers being repelled as they reached the Lancastrian's defensive ditch.
However, Warwick had been in secret negotiations with Lord Grey of Ruthin, who was fighting for the King. As March and his men approached his side of the defensive line, Grey switched sides and his men helped the Yorkists across the ditch and through the fence.
This treachery, sealed in return for land, was enough to win the battle. Now attacked from its right flank, the Lancastrian army was quickly defeated with many armour-clad troops drowning as they tried to flee across the River Nene.
All of the main Lancastrian leaders were killed and King Henry VI was captured and led back to London.
In the aftermath, Richard of York returned from Ireland to push his dynastic claim to the throne. However, he was rebuffed and killed in battle within the year.
The 18-year old Edward, Earl of March, was Richard's son and Northampton had been his first battle. He took on his father's mantle and just a year later became Edward IV, King of England.
Join our tour: the battlefield of Northampton is one of the key locations we explore in our new Wars of the Roses tour. Led by Mike Ingram, who has written extensively on the Wars, you'll enjoy exclusive access to the sites and unrivalled insight into the people, politics and military tactics.
For Wars of the Roses tour details and daily itinerary
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Picture credit: The Battle of Northampton by historical illustrator Matthew Ryan.