Pope Francis said on Saturday the spate of conflicts around the globe today were effectively a "piecemeal" Third World War, condemning the arms trade and "plotters of terrorism" sowing death and destruction.

"Humanity needs to weep and this is the time to weep," Francis said in the homily of a Mass during a visit to Italy's largest war memorial, a large, Fascist-era monument where more than 100,000 soldiers who died in World War One are buried.

The pope began his brief visit to northern Italy by first praying in a nearby, separate cemetery for some 15,000 soldiers from five nations of the Austro-Hungarian empire which were on the losing side of the Great War that broke out 100 years ago.

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"War is madness," he said in his homily before the massive, sloping granite memorial, made of 22 steps on the side of hill with three crosses at the top.

"Even today, after the second failure of another world war, perhaps one can speak of a third war, one fought piecemeal, with crimes, massacres, destruction," he said.