Pope Benedict called for Christian unity when he joined the spiritual head of Orthodox Christians on Saturday to launch a year dedicated to St. Paul, the evangelist of the early Church born two millennia ago.

The Pope presided over the ceremony at Rome's Basilica of St. Paul's Outside the Walls, which houses a marble sarcophagus believed to contain the remains of the 1st century apostle.

It is the second largest of Rome's basilicas, after St Peter's in the Vatican.

"We, although being many, are one body only," the Pope said, referring to the ties that unite Christians.

He was joined by Ecumenical Patriarch Bartholomew, the spiritual head of worldwide Orthodoxy, which split from the Roman Catholic Church in 1054.

St Paul was born in the city of Tarsus in present-day Turkey. He persecuted early Christians but converted when he had a vision on the road to Damascus years after Christ's death and became known as the "apostle to the gentiles".

According to Catholic tradition, St Paul was killed for his faith in the 1st century and buried on Rome's Via Ostiense.

Pope Benedict has met Bartholomew several times with the goal of healing the rift between the Catholic and Orthodox Churches.

"St Paul reminds us that the full communion among all Christians finds its grounds in a single father, a single faith and single baptism," Pope Benedict said in an address to Bartholomew earlier on Saturday.