VATICAN CITY-Pope Benedict XVI and Ecumenical Patriarch Bartholomew I renewed their appeals for Christian unity on Sunday during a Mass in St. Peter's Basilica.

Benedict led the ceremony alongside the leader of the world's 250 million Orthodox Christians and expressed the "common hope of seeing the day of unity draw near."

While acknowledging key differences, Benedict has made healing the 1,000-year-old rift with the Orthodox a priority of his papacy.

In his speech, Bartholomew said that dialogue between the two branches of Christianity is continuing, despite "numerous difficulties" and that he was praying for these obstacles to be overcome.

After centuries of moving apart, the two churches formally split in 1054 over several issues, including the primacy of the pope, devotional differences, and Latin demands for priestly celibacy as the Greek-influenced tradition permitted married clergy.

Relations remain tense over Orthodox charges of proselytizing and rival property claims in places such as Russia and eastern Europe. However, Benedict and Bartholomew have met several times in an effort to promote or to seek a reconciliation.

Benedict, the leader of the world's 1 billion Roman Catholics, told the crowd that Christian unity is even more important in a world that is increasingly connected by technical means, but is unable to resolve its conflicts.

"In today's world there are new instruments of unity which, however, also create new conflicts and give new strength to old ones," he said.

"In the midst of this external unity, based on material goods, we have an even greater need for interior unity, which comes from the peace of God."

The Mass marking the feast of St. Peter and St. Paul included readings from the Gospels in Latin and Greek by Catholic and Orthodox clerics. Benedict and Bartholomew also prayed together in Greek.

During the ceremony Benedict bestowed the pallium, or a woolen shawl, on 40 archbishops from around the world to symbolize their bond with the Vatican. One by one the archbishops, wearing crimson vestments, knelt before the pope to receive the shawl and the pontiff's embrace.

After the Mass, Benedict and Bartholomew silently prayed together underneath the basilica at the tomb the faithful believe houses the remains of the apostle Peter.