The Archbishop of Canterbury and Pope Benedict XVI jointly prayed for the unity of Christianity in a rare gesture on Saturday despite simmering resentment over the Catholic Church's move to recruit Anglicans.

Anglican leader Rowan Williams and the pope celebrated vespers together in the monastery of San Gregorio al Celio near the Colosseum in Rome and a stone Celtic cross brought from Canterbury was put up in the ancient church.

The late pope John Paul II had held ecumenical prayers with the Anglican archbishop's predecessors Robert Runcie in 1989 and George Carey in 1996.

In his homily Williams said the Church was "called upon to show that same prophetic spirit which is ascribed to St Gregory, the capacity to see where true need is and to answer God's call in the person of the needy.

"To do this, it requires a habit of discernment, penetration beyond the prejudices and cliches which affect even believers in a culture that is so hasty and superficial in so many of its judgements."

Christians should set "aside the distortions in our vision that are caused by selfishness and greed", he said.

"In recent years, we have seen developing a vastly sophisticated system of unreality, created and sustained by acquisitiveness, a set of economic habits in which the needs of actual human beings seem to be almost entirely obscured."

Williams also warned against "a feverish advertising culture in which we are persuaded to develop unreal and disproportionate desires".

"We are all, Christians and their pastors included, in need of the discipline that purges our vision and restores to us some sense of the truth of our world, even if that can produce the ?torment' of knowing more clearly how much people suffer and how little we can do for them by our unaided labours," he said.

Benedict said the icon which he placed inside the church and the stone cross should prompt Catholics and Anglians visiting the tombs of the "apostles and martyrs... to pray and act in favour of (Christian) unity".

There have been tensions, however, following Benedict's move in 2009 to set up special structures in Britain and the United States to allow disgruntled conservative Anglican clergymen and faithful to join the Roman Catholic Church.

But Vatican spokesman Federico Lombardi has said the prayers, as well as two joint performances by the choirs of Westminster Abbey and the Vatican later this month, were "a sign of moving together along the same path".

The San Gregorio monastery of Camaldolese monks has developed close ties with the Anglican Church since it was from here that pope Gregory the Great sent out 40 monks in the sixth century to evangelise Britain.