Prince Rainier III of Monaco is to be laid to rest today beside his late wife, the American film star Grace Kelly, in the cathedral where they were married a half century ago.

In line with Rainier's wishes, the funeral will be intimate, with family and about 150 guests -- including kings, princesses, presidents, diplomats and dignitaries from some 60 countries.

For many in Monaco, where Rainier ruled for 56 of his 81 years, the day marks the end of a golden era. Rainier and Kelly were wed in the cathedral in 1956 -- a union that became the tiny Mediterranean principality's claim to fame.

Rainier never remarried after Princess Grace's death in a car accident in 1982 -- and often cut a lonely figure in his latter years. An empty slab of marble beside Grace's resting place in the family crypt has been waiting to be engraved with the monarch's name.

Royal pomp was to be mixed with solemn Roman Catholic ceremonies and tight security for the afternoon funeral.

Dignitaries will pay respects to the late leader at the royal palace's 17th century Palatine Chapel, where his body has lain in state since last weekend. Rainier died on April 6 of heart, kidney and breathing problems after struggling with failing health for years.

From the chapel, the VIPs will be escorted to the palace's official reception hall, the ornate Blue Salon, to pay condolences to Rainier's son and heir, Prince Albert II, and his daughters, the Princesses Caroline and Stephanie.

A public procession begins at that point, beginning with visiting guests. VIPs will walk across the palace's cobbled square and down a narrow lane now hung with Monaco's flags at half staff to the nearby 19th century Monaco cathedral.

As Rainier had requested, 10 soldiers from the Prince's Company of Carabineers will bear his coffin out of the palace via the Gate of Honour shortly before noon (1000GMT), crossing a square filled with up to 3,000 mourning Monaco residents, before reaching the cathedral.

Members of the royal family will follow the procession as a band plays Beethoven's Funeral March -- music chosen by Princess Caroline. A battery will fire a 36-gun salute for Rainier, who had been Europe's longest-serving monarch.

Monaco Archbishop Bernard Barsi will lead the 90-minute religious ceremony in the cathedral that will be broadcast on live television and shown on large screens outside a half-dozen churches. He plans to say that Rainier "has entered the shadow of death: May the light of the Saviour now rise upon him," according to a transcript released by the palace.

Some 1,300 police will provide security. Funeral wreaths were being scanned for bombs. Monaco's harbour and air space will be closed during the funeral.

All shops and businesses in Monaco, including its fabled Monte Carlo Casino, were to be closed today to mark a day of national mourning.

Matches at the Monte Carlo Masters tennis tournament were to be delayed until 2.30pm (1230GMT) out of respect for the prince's funeral.

More than half a dozen heads of state were expected at the funeral: French President Jacques Chirac, Irish President Mary McAleese, Belgium's King Albert II, Luxembourg's Grand Duke Henri, Spain's King Juan Carlos and Queen Sofia, Sweden's King Carl XVI Gustaf and Queen Silvia, Slovenian President Janez Drnovsek and San Marino's Capt. Regents Fausta Simona Morganti and Cesare Antonio Gasperoni.

Other dignitaries who confirmed attendance include Britain's Prince Andrew.

Only Rainier's close family will attend his burial tonight in a private ceremony. The family crypt also holds the remains of Rainier's three immediate successors: Prince Charles III, who ruled from 1856 to 1889; Prince Albert I, who ruled from 1889 to 1922; and, Rainier's grandfather, Prince Louis II, who ruled from 1922 to 1949.