A "complex" security operation has been put in place for the opening of the Welsh assembly's Senedd building, say South Wales Police.
The Queen, Duke of Edinburgh, Prince Charles and the Duchess of Cornwall will officially open the £67m debating chamber in Cardiff Bay on Wednesday.
Police leave has been cancelled and officers from other forces are in the city to prepare for possible protests.
Chief Superintendent Graham Davies said: "It will be a testing day."
South Wales Police have described the Senedd opening as "an iconic event in Welsh political history, attracting attention from across the globe".
The force has warned that people living in the bay area should expect some disruption as part of a "high visibility police presence" during the day's events.
In November 2004, South Wales Police ran a week-long security operation ahead of the gala opening of the Wales Millennium Centre, also on the Cardiff Bay waterfront.
The Queen, Duke of Edinburgh and Prince Charles attended that event, which the force also described as "iconic" and unusual for having all three royals at the same public location at the time.
On Tuesday, Chief Superintendent Davies is to outline the advice to the public while current security arrangements are in place.
He said: "It will be a testing day. This is a significant day for Wales and the spotlight of the world will be on us. It's trying to keep a balance."
He said the force had prepared for possible protests ahead of the Senedd opening, although he said this had put a "definite strain on policing".
Rhodri Morgan addresses AMs during the first session
"This is an historic event for Wales, part of a new Welsh democracy and if people decide to exercise their right to peaceful protest we hope they stay within the law," he said.
"It's a complex operation - we have to allow the public a right of access as much as possible and we're trying to make searching the building as unobtrusive as possible."
In addition to the Senedd ceremonies on Wednesday, Cardiff also hosts an international football match as Wales meet Paraguay at the Millennium Stadium.
In September 2005, Gwent Police coordinated more than 1,500 police and security officers for the two-day EU foreign ministers' meeting at the Celtic Manor Resort, Newport.