WARSAW, Poland - A collection of letters written by popes and kings some 700 years ago that was found among the possessions of a deceased US World War II veteran was turned over Monday to Polish national archives officials.

Neal Pease, a history professor at the University of Wisconsin in Milwaukee, handed the box of documents to Wladyslaw Stepniak, deputy head of Poland's National Archives, soon after arriving at Okecie airport in Warsaw.

Neal Pease, history professor at University of Wisconsin in Milwaukee, right, presents a box containing 17 letters dating back to the 13th century to Professor Wladyslaw Stepniak, deputy head of Poland's National Archives, at Okecie airport in Warsaw, Poland Monday, Aug. 28, 2006. Pease returned the manuscripts, some written by popes and kings, to Poland Monday, after they were lost in the evacuation of the southwestern city of Wroclaw during World War II and brought to Milwaukee by a U.S. soldier who found them in 1945. [AP]

"We are very, very grateful. These letters are of great value to us," Stepniak said in accepting the box.

"It's a great honor," Pease replied. "I am relieved and very glad that they are back home."

Stepniak and an archivist accompanying him declined to open the box at the airport to show its contents out of concern for the documents.

The letters, some dating back as far as 1256 and primarily recording real estate transactions, surfaced when a Wisconsin man found them among the belongings of his father, George G. Gavin, a WWII veteran who had brought them home as a souvenir of his wartime service in Europe.

After his father's death, Philip Gavin entrusted the letters to the Archives of the Roman Catholic Archdiocese of Milwaukee, which had them authenticated in 2003.

Gavin then decided they should be returned to where they came from, which - according to stamps they bear - was the archives of the city of Wroclaw, in southwestern Poland.

An official ceremony marking the handover of the letters was scheduled for Thursday at the National Archives in Wroclaw.

Wroclaw was the German city of Breslau before World War II but came under Polish rule when the borders were shifted westward when the war ended. The letters were likely lost in transport near the end of the war when the Germans were evacuating the city to flee the advancing Red Army.

Gavin said his father recovered the documents from the mud by a burned-out train in Austria, and Pease said there was no reason to doubt the report.