Pope Francis will honor the dead from both sides of World War I during a visit next month to northern Italy that witnessed some of the decisive final battles of the conflict — and where his own grandfather battled.

On Sept. 13, Francis will lay a wreath at the Austro-Hungarian cemetery in Fogliano di Redipuglia, near Gorizia on Italy's border with Slovenia. He will then celebrate Mass at the nearby Fascist-era memorial to 100,000 Italian dead.

The Vatican said Thursday that Francis would pray for the victims of all wars during the visit, his main commemoration of the 100th anniversary of the start of World War I.

While Italy was technically part of the Triple Alliance with Austria-Hungary and Germany at the start of the war, it remained neutral until declaring war on Austria-Hungary in May, 1915 after a series of secret negotiations with Britain and France. More than 600,000 Italians were killed over the next three years, with the Battle of Caporetto in October, 1917 one of the deadliest of the entire war.

Francis has previously said he recalls hearing "many painful stories from the lips of my grandfather," who fought in the war.

The pope's paternal grandfather, Giovanni Carlo Bergoglio, was drafted into the war at the age of 30 with a regiment along Italy's border with Slovenia, according to documents unearthed by the newspaper and TV station of the Italian bishops' conference.

The elder Bergoglio fought in several battles during the subsequent years and at the war's end obtained a certificate of good conduct and 200 lire.

He returned to civilian life in Piedmont, but immigrated to Argentina a decade later, as Italy's post-war economy struggled to recover.