A medieval castle's 600-tonne wall collapsed on to a house and garden in Lewes sparking a major search.
Emergency services, including a hazardous area response team and sniffer dogs, went to the scene of the collapse of the 10m (32ft) by 10m wall.
When the alert first came in at 12:22 GMT, it was not known if anyone was trapped and dogs trained for use in earthquake zones were deployed.
Firefighters later tweeted the search was over with no casualties found.
Incident commander Matt Lloyd said the wall had fallen into an adjacent garden and house.
The wall had been reportedly undergoing work to remove ivy in recent weeks.
A spokeswoman for castle owners Sussex Archaeological Society said the wall that collapsed was privately-owned and the section that had fallen was part of the curtain wall that ran round the entire outside of the 1,000-year-old landmark.
It was one of the last remaining sections of the historic defence wall, she said, adding: "There's not much of it left standing. It's one of the last sections that was still at full height."
We are drawing the search at #Lewes castle to a close - no casualties have been found or reported. We will be leaving the area shortly. Thank you to everyone who has worked so hard today. https://t.co/dT8VjnsaMp pic.twitter.com/CGCOjjcrA0— East Sussex FRS (@EastSussexFRS) November 11, 2019
Staff at the castle closed the attraction on Monday as a precautionary measure, the spokeswoman said.
She said the castle walls that are owned by the archaeological society are checked independently on an annual basis.
Several parts of the castle structure are privately owned by different property owners.
Lewes District Council said officers from its building control team went to the scene to liaise with emergency services.