Eight 13th-century catapult shots have been discovered perfectly preserved outside the walls of Kenilworth Castle in Warwickshire.

These would have been fired from a catapult during the siege of Kenilworth Castle 1266, when England faced a civil war.

The stone spheres are of varying sizes, with the largest weighing 105kg and the smallest just 1kg. The discovery was made during a major project to improve accessibility around the castle.

Between 25 June and 13 December 1266 for a total of 172 days, Kenilworth Castle was under constant attack in one of the most significant military contests of Henry III's reign.

The king's conflict with his nobles had escalated into civil war some years before. The leader of the rebels was the king's own brother-in-law Simon de Montfort, Earl of Leicester, who had custody of Kenilworth Castle.

When Montfort was killed in August 1265 at the Battle of Evesham, his supporters continued to use Kenilworth as a base. In March 1266, Henry's messenger to the rebels was returned to him with a severed hand. Outraged, Henry then attempted to reclaim the former royal stronghold by force.

The king used a large arsenal of weaponry in his attacks on Kenilworth, including 60,000 crossbow bolts and nine siege engines including catapults, in an attempt to breach the 14-feet thick walls of the castle.

However, the garrison inside had also equipped themselves with similar siege engines. It is the stone projectiles that were being fired from both sides that have been found outside the west castle walls, close to the ground's surface.

After almost six months, the resistance efforts of the rebels fell to starvation and disease, and surrendered Kenilworth Castle to Henry, who then gave it to his son, Edmund, Earl of Lancaster.

Will Wyeth, English Heritage's Properties Historian said, 'We were able to immediately link these findings to the 1266 siege because of similar finds recovered during an archaeological excavation of Kenilworth Castle in the 1960s.

'However, it's not every day we get lucky enough to stumble across historical remains like this by chance. Imagine the surprise of the team working on improving the pathways around the site when they unearthed these impressive stone projectiles that are nearly 800 years old!

'These would have caused some serious damage fired from war machines. Records show that one of Henry III's wooden siege towers, containing around 200 crossbowmen, was destroyed by just one well-aimed missile.'

Kenilworth Castle has been undergoing work over the past four months to improve accessibility around the site for pedestrians and wheelchair users, including on permissive pathways outside the site that are cared for by English Heritage. The improvements have been generously funded by a grant from the FCC Communities Foundation, together with support from local organisations.

Archaeology Warwickshire, led by Dr Cathy Coutts, were commissioned by English Heritage to monitor and record any archaeology uncovered during the groundworks.

Dr Coutts, Principal Historic Buildings Officer at Archaeology Warwickshire added, 'Once the project contractors had found one catapult shot, our archaeologist on site was then able to uncover a further seven as the works around the castle progressed.

'As these shots were found pretty much where they would have fallen, we've been able to extrapolate where the siege camps could have been located around the castle, which has been exciting to consider.'

• Find out more about and book to visit Kenilworth Castle here.