The service took the form of midday prayers with psalms sung in plainsong, in the presence of senior Vatican representatives, including Cardinal Walter Kasper and Cardinal Cormac Murphy O'Connor, and senior Anglicans including Archbishop Peter Carnely and Bishop David Beetge.

The Redemptoris Mater Chapel, formerly known as the Matilde Chapel, was rededicated by Pope John Paul II in 1999 after nearly four years of restoration work.

After the service Pope Benedict hosted a private lunch for Dr Williams.

Earlier, in a Common Declaration signed by Pope Benedict and Dr Williams, the two leaders expressed thanks for forty years of cooperation and dialogue between the Roman Catholic Church and the churches of the Anglican Communion and renewed the historic commitment to the goal of 'full visible communion in the truth of Christ'. The two paid tribute to the continuing process of dialogue, which had begun with the historic meeting between Pope Paul VI and Archbishop Michael Ramsey in 1966:

"Since that meeting, the Roman Catholic Church and the Anglican Communion have entered into a process of fruitful dialogue, which has been marked by the discovery of significant elements of shared faith and a desire to give expression, through joint prayer, witness and service, to that which we hold in common."

As that process continues, the Declaration acknowledged, difficulties and obstacles to this goal caused by new developments within the Anglican Communion would need to be faced:

"... in renewing our commitment to pursue the path towards full visible communion in the truth and love of Christ, we also commit ourselves in our continuing dialogue to address the important issues involved in the emerging ecclesiological and ethical factors making that journey more difficult and arduous."

The Churches share a common witness and service, the statement said. There were issues and challenges, which could be tackled jointly:

"There are many areas of witness and service in which we can stand together, and which indeed call for closer co-operation between us: the pursuit of peace in the Holy Land and in other parts of the world marred by conflict and the threat of terrorism; promoting respect for life from conception until natural death; protecting the sanctity of marriage and the wellbeing of children in the context of healthy family life; in outreach to the poor, oppressed and the most vulnerable, especially those who are persecuted for their faith; in addressing the negative effects of materialism; and in care for creation and for our environment. We also commit ourselves to inter-religious dialogue through which we can jointly reach out to our non-Christian brothers and sisters."

The Common Statement concluded with a reminder of the Churches' common calling:

"Confident of the apostolic hope "that he who has begun this good work in you will bring it to completion"(Phil 1:6), we believe that if we can together be God's instruments in calling all Christians to a deeper obedience to our Lord, we will also draw closer to each other, finding in his will the fullness of unity and common life to which he invites us."

During the Audience, Dr Williams praised the ecumenical commitment of Pope Benedict XVI in a formal greeting presented to the Pope:

"I have been heartened by the way in which from the very beginning of your ministry as Bishop of Rome, you have stressed the importance of ecumenism in your own ministry. If the Good News of Jesus Christ is to be fully proclaimed to a needy world, then the reconciliation of all Christians in the truth and love of God is a vital element for our witness."

He acknowledged the difficulties and obstacles to unity and said that churches were affected by each other's troubles:

"I say this, conscious that the path to unity is not an easy one, and that disputes about how we apply the Gospel to the challenges thrown up by modern society can often obscure or even threaten the achievements of dialogue, common witness and service. In the modern world, no part of the Christian family acts without profound impact on our ecumenical partners; only a firm foundation of friendship in Christ will enable us to be honest in speaking to one another about those difficulties, and discerning a way forward which seeks to be wholly faithful to the charge laid upon us as disciples of Christ."

Anglicans and Roman Catholics shared a charge, he said, to serve Christ in the preaching of the Gospel:

"However, there is a task which is laid upon us both as pastors of the Christian family: to be advocates of reconciliation, justice and compassion in this world - to be ambassadors for Christ - and I am confident that an honest exchange of our concerns will not be allowed to eclipse what we can affirm and proclaim together - the hope of salvation and healing found in the Grace and Love of God revealed in Christ."

During the Audience, Dr Williams presented the Pope with a specially commissioned icon showing St Gregory and St Augustine - forbears of Pope and Archbishop of Canterbury respectively - in the presence of Christ the Saviour, Lord of the earthly and heavenly realms. The icon has been painted by Sergei Fyodoro, a Moscow-based iconographer. Further details are below.

Earlier in the day, Dr Williams and the Anglican Delegation said prayers in St Peter's Basilica at the Tomb of Pope John Paul II, whose funeral Dr Williams attended in 2005.