A blaze thought to have been caused by a fireball which was launched from a trebuchet at Warwick Castle has destroyed a historic boathouse.
Sparks from the projectile are believed to have ignited the blaze.
About 300 spectators were watching a demonstration of the weapon, described as the "world's largest working siege machine", when the thatched building caught fire on Friday evening.
"No-one was ever at any risk," a castle spokeswoman said.
Eyewitness Dr Martin Lees, 45, from central London, was watching with his wife and two six-year-old boys, from across the River Avon.
He said there was "more concern than panic" among fellow spectators.
"There was a bit of a wind. The breeze picked up the ash and a bit of ash was coming down on our side of the river," he said.
"It was intriguing more than anything else... It was well-managed by the staff."
Dr Lees said the large projectile, which looks like a "bag of cement" set on fire, landed at least 10m (33ft) away from the boat house at the climax of the demonstration.
He said: "I'd say it was about three minutes between the projectile landing on the grass and the fire starting at the boat house.... I suspect sparks from that landed on the roof.
"It's just possible it's not related to this but it seems unlikely."
The castle said "despite speculation" it had not yet ascertained the cause of the fire and the island housing the boat house was not open to the public.
The Trebuchet Fireball Spectacular was built in 2005, is 60ft (18m) high, weighs 22 tonnes and has been fired at least 6,500 times, while the boat house dates back to 1896.
In a statement, the castle spokeswoman said the fire, which began at about 17:45 BST, was "was safely extinguished within a short time".
She said people watching on the opposite side of the River Avon were moved away from the bank.
An internal investigation was under way and the castle was fully open on Saturday, she added.