The May 7 ceremony, announced Friday by the Vatican, will also honor persecuted Catholics in Spain and Mexico and Asian missionaries.
The names to be honored include not only Roman Catholics, but also Orthodox Christians and Protestants, the Vatican said, part of the pope's efforts to bring divided Christian churches closer together. The Vatican did not say when it would release a list of honorees.
Rev. Martin Luther King Jr., the slain American civil rights leader who was a Baptist, and Oscar Romero, the slain Salvadoran Catholic archbishop, were reportedly on the list of more than 12,000 names sent to the Vatican for consideration from bishops around the world.
Vatican officials said the commemoration is part of the pope's efforts to hold up as models Christians who died for the faith, but that it is entirely separate from any individual beatification or canonization process.
``The witness to Christ born even to the shedding of blood has become a common inheritance of Catholics, Orthodox, Anglicans and Protestants,'' said Bishop Piero Marini, in charge of papal ceremonies.
The Colosseum was the site of deaths of gladiators and wild beasts in ancient Rome, and some say early Christians were martyred there.
A hint at the identity at those being honored were the categories of those whom the Vatican described as the ``witnesses to faith'' in the 20th century.
The categories include:
Those who suffered under Soviet totalitarianism and communism; victims of Nazism and fascism; missionaries in Africa, Asia and Oceania; those persecuted ``out of hatred for the Catholic faith'' in Spain and Mexico; and Christians martyred in the Americas and other parts of the world.