Tens of thousands of Africans have trekked to a shrine in the central Ugandan town of Namugongo to mark Martyrs' Day, the largest religious event in east Africa.

The annual event coincides with the Catholic feast day for saints Joseph Mukasa and Charles Lwanga. They were two of 45 Protestant and Catholics put to death by the Ugandan king, Mwanga, in the late 19th century.

All of them are commemorated by the more ecumenical Martyrs' Day celebration which was celebrated on June 3 by the Roman Catholic Church.

"The Martyrs are heroes and models for us, as the faithful, to follow in our faith. They were given choices: 'Denounce Christianity or die.' They chose 'to die rather than denounce their faith'," said the Uganda Episcopal Conference representing the country's Catholic bishops on their website.

King Mwanga II was 18 years old when he succeeded his late father to the Ugandan throne in 1884.

It was a period when Christians and Moslems were competing to convert local people.

And while his father, King Mutesa I, had been friendly to both Christian missionaries and Ugandan converts, Mwanga saw Christianity as a threat to his power.

Furthermore, Mwanga was sexually abusing young pages in his court, many of whom had converted to Catholicism.

The first martyr was Joseph Mukasa, the king's chief page, who was beheaded for trying to protect the boys from the king.

Charles Lwanga became the chief page, and he also tried to protect his young wards from the king, also secretly baptizing four of them.

When Mwanga learned of the baptisms, he questioned Lwanga and the pages - 15 young men in all - asking them about their faith.

When they responded they would remain Christians "until death," the king had them sent to Namugongo to be executed.

On June 3, 1886, those who had night died on the 37-mile trip were burned alive, setting off the two-year wave of persecution that left 45 Christians dead.

The 22 Catholic martyrs were canonized by Pope Paul VI in 1964.

St. Joseph Mukasa is the patron saint of chiefs and politicians, and St. Charles Lwanga is the patron saint of African Catholic Youth Action, converts and torture victims.

Today, Uganda is more than 80 percent Christian, split evenly between Catholics and Protestants.