IN LONDON it is the Tomb of the Unknown Warrior in Westminster Abbey. In St Petersburg it is the mass graves of the 900-day Siege of Leningrad. In New York, the first port of call for any prominent visitor is Ground Zero.

Yesterday the Prince of Wales and the Duchess of Cornwall began an eight-day US tour with a visit to the shrine in downtown Manhattan that commemorates the worst attack on the American homeland since Pearl Harbor, in which 67 Britons were among the 3,000 who died in one of the blackest days of the country’s history.

Fresh from a six-hour flight from RAF Lyneham in Wiltshire, the royal couple were taken straight to the site of the World Trade Centre, in the heart of the city’s financial district, to be met by Sir Philip Thomas, the British Consul-General in New York, George Pataki, the Governor of New York State, and Kenneth Ringler, executive director of the New York Port Authority, which owns the site.

As they arrived at the 16-acre Ground Zero site, a Union Jack pulled from the rubble of the September 11 tragedy fluttered above the memorial.

During their 20-minute visit the Duchess performed the first act of her first official overseas tour as wife of the heir to the throne when she laid a bouquet of yellow and orange flowers bearing a card handwritten by the Prince and signed by them both bearing the message: “In enduring memory of our shared grief.”

The Duchess looked nervous at the start of her highest profile engagement since her wedding. She wore a red Italian wool crepe jacket and dress with velvet and chiffon trim, designed by Roy Allen. She was hatless. In a room at the site set aside for those who find a visit too troubling, the Prince and the Duchess had a private meeting with relatives of some of the British victims.

Three blocks away several hundred peoplegathered in the small Manhattan square where the couple performed their next engagement at the British Memorial Garden, which is still being built. They were cheered as they stepped from their car, and immediately performed an impromptu walkabout, to the delight of New Yorkers.

For the royal couple it was a sombre start to a tour that will take them to a black-tie dinner with the Bushes at the White House, visits to disadvantaged people of Washington, a brief look at the hurricane damage in New Orleans and an inspection of organic farming outside San Francisco.

Although a weekend opinion poll suggested that Americans were overwhelmingly indifferent to their first opportunity to inspect the Prince’s new bride, the tour is of major importance to him. Americans, both individual and corporate, are significant contributors to his charities and he feels it essential to maintain a high profile and to gain acceptance for his wife.

Twenty years ago his American tour with Diana, Princess of Wales, was all glitz and glamour, and she stole the show. This visit is far more serious and worthy, with the Duchess fully aware that she is the supporting act, not the star.

The earnestness of the present tour was in evidence the moment the couple left the Memorial Garden. They went to the United Nations, where, after meeting Kofi Annan, the Secretary-General, the Prince addressed a seminar on youth enterprise. A handful of Diana fans protested outside the building.

Times Recommends

• Gloves off as McCain lands Obama 'lie' jibe
• Anger as terrorist gets bail for IVF
• US hands palace of Saddam back to Iraqis