Archbishop Rowan Williams spoke of the "certain but imperfect" link between the two Christian traditions during his address to the congregation at a joint service at the church of St Gregory the Great near Rome's Colosseum.
The 84-year-old German pope, who earlier held a private meeting with the archbishop at the Vatican, urged all Christians to "renew their commitment to pray constantly and to work for unity" at the same service.
Past popes and Anglican leaders have been much more outspoken about their differences - over issues ranging from women priests and homosexuality to church doctrine - during their meetings.
...The choice of the church for the joint service was symbolically significant because it was from there that the sixth century Pope St Gregory sent out monks to convert the English. The monks included the man who became St Augustine, the first Archbishop of Canterbury.