Pope John Paul II preached about the virtues of monogamy Friday at a Mass attended by the 20-year-old king and his four wives.

King Mswati III, the world's youngest monarch, sat expressionless as the pope said God intended each husband to have one wife.The pope arrived at the capital's national stadium in his popemobile escorted by spear-carrying warriors. He spoke from an altar topped by a turret holding a soldier with a rifle and binoculars. A cross on the structure was stamped with a spear, shield and war ax.

"Christians find that a monogamous marital union provides the foundation upon which to build a stable family in accordance with the original plan of God for marriage," the pope told a crowd of about 10,000 in the national stadium.

"Hence, any forms of disregard for the equal dignity of men and women must be seen as serious contradiction of the truth that Christ, the king of peace, brought into the world," he said.

Vatican sources said John Paul was warned by local prelates to tread carefully before addressing the issue of polygamy, but he went ahead anyway.

An estimated 70,000 of Swaziland's people - roughly 10 percent of the population - are Catholics, but the king is not one of them.

Mswati has never issued any statement on his religious beliefs. His father supported freedom of religion and said he was a member of all religions. Mswati is believed to follow in the same tradition.

Later Friday, the pope went on to Mozambique, the last stop on a 10-day visit of southern Africa that also included Zimbabwe, Botswana and Lesotho. He urged Mozambique's Marxist government to negotiate with rightist rebels.

Swaziland, a stable country of 700,000 people wedged between South Africa and Mozambique, is a dual monarchy under the king, offically known as the Lion, and a queen mother called the Great She Elephant.

Polygamy is no longer practiced extensively in Swaziland, but it is a tradition in the royal family.

The Mass was unusual from the start. John Paul's open-topped popemobile was driven in the wrong direction after it circled once around the track at the stadium.