The new Pope Benedict XVI will be officially installed during the inauguration mass this Sunday at St Peter's Square, Rome. More than 500,000 people along with state leaders across the world are expected to join this historical occasion that will mark a new era of the Roman Catholic Church, Rome's Mayor, Walter Veltroni said on Thursday.

The mass will start at 10:00 local time (09:00 BST), the Vatican announced on Tuesday. The 78-year-old former Cardinal Joseph Ratzinger of Germany will be inaugurated as the Roman Catholic Church’s 265th pontiff and has chosen the name Benedict XVI. The name comes from the Latin word for "blessing".

Pope Benedict XVI was once the Archbishop of Munich. German President Horst Koehler and his spouse as well as Chancellor Gerhard Schroeder and his wife are expected to honour their fellow countryman.

From the UK, the Archbishop of Canterbury Dr Rowan Williams will travel to Rome on Saturday, accompanied by the Revd Andrew Norman, Archbishop’s Secretary for International and Ecumenical Affairs, and the Revd Jonathan Jennings, the Archbishop’s Press Secretary.

Archbishop Rowan will become the first serving Archbishop of Canterbury to attend such an occasion, at least since the Reformation. The Pontifical Council for Promoting Christian Unity has warmly welcomed his attendance.

The Archbishop has confirmed in a statement released today that he will be wearing the ring presented to his predecessor, Archbishop Michael Ramsey, by Pope Paul VI and a pectoral cross presented to him by Pope John Paul II.

Other leaders such as French Prime Minister Jean-Pierre Raffarin, French Foreign Minister Michel Barnier, Portuguese Prime Minister Jose Socrates, Belgium Prince Philippe and his wife Princess Mathilde, Spanish royalty as well as President of Colombia Alvaro Uribe will be present at the ceremony.

An estimated 700,000 other pilgrims are also expected to fill the surrounding streets near St Peter's Square to watch the ceremony on giant screens.