Barriers have been installed and security enhanced around Windsor Castle during the Changing Of The Guard following the Westminster terror attack.
Barriers went up around the royal residence in Berkshire on Monday - forming a ring of steel - to support existing road closures while the ceremony is under way, Thames Valley Police said.
The force said the changes were "proportionate and necessary" but said there was "no specific threat to Windsor".
The next Changing Of The Guard - a popular tourist attraction - will take place on Wednesday.
Assistant Chief Constable Dave Hardcastle said: "While there is no intelligence to indicate a specific threat to Windsor, recent events in Westminster clearly highlight the need for extra security measures to be introduced.
"Preventative measures such as these have been put in place across the UK over the past 10 years at various events.
"The national threat level remains severe, which it has been since 2014, and I would urge the public to be alert to the threat of terror attacks but not alarmed, and to remain vigilant."
The new barriers will only be used to secure the route of the procession during the event and will remain open at other times.