Security: Kings, queens, prime minister and presidents will be at the funeral. Tom Clonan examines a security nightmare.
The combination of a large number of heads of state and government in the one place - a very confined area - at the one time poses a considerable security challenge to the Italian and Vatican authorities.
In the light of the international terrorist threat posed by groups such as al-Qaeda, which have a penchant for striking during sensitive religious ceremonies - such as during the Shia Ashura celebrations in Iraq and Pakistan over the past two years - the US presidential party of George Bush will have to rely on close co-operation with the Vatican's security services in order to guarantee the president's safety.
In terms of internal security, the Vatican - an autonomous independent state - has its own army in the form of the Swiss Guard. Consisting of approximately 100 men, the Swiss Guard is normally associated with its striking Medici-designed uniform, renaissance helmet and mediaeval halberd - a large axe-like weapon carried during ceremonial duties. Trained in the Swiss armed forces, these guards will assume a high-profile role during the funeral ceremonies in the coming days.
However, the primary responsibility for security within the Vatican for tomorrow's funeral will rest with the Holy See's police force, the Servizio di Vigilenza.
This highly-trained security force will liaise closely with the Italian authorities to ensure an integrated and co-ordinated approach to Vatican security at all levels. In this regard, the Vigilenza are overseen by the Vatican's deputy secretary of state or "sostituto" with responsibility for the curia and the internal affairs of the city-state. The sostituto in turn liaises directly with the Vatican's foreign minister, who enjoys a healthy relationship with the US Central Intelligence Agency.
The CIA and US military intelligence services will in turn work closely with their Italian counterparts to protect the US presidential party. Counter-terror measures for the funeral have been hastily improvised but are thought to be sufficiently robust to protect the heads of state and government, together with the many religious leaders from around the world who will be participating in the funeral ceremonies.
Such measures include an air-exclusion zone over Rome from today, the deployment of anti-aircraft and anti-missile batteries around the Vatican as well as aggressive patrolling by Nato and US Air Force aircraft based at Aviano.
On the ground, in addition to a significantly-reinforced Italian police presence, 6,500 heavily-armed carabinieri will form a protective ring around the ceremonies.
In a departure from precedent - and in testimony to the close relationship which exists between the Vatican and the US administration - the secret service detachment guarding the US presidential delegation will retain their personal weapons within St Peter's Square.