A collection of 13th Century letters, found among the belongings of a US World War II veteran, has been returned to Poland.
The letters are of great value
Some of the letters were written by popes and date as far back as 1256.
They were discovered by Philip Gavin from Wisconsin after the death of his father, George Gavin, who brought them home as a souvenir of the war.
They are from the archives of Wroclaw, south-western Poland, which was the German city of Breslau before WWII.
They were handed over in a box by Neal Pease, history professor at the University of Wisconsin, to Wladyslaw Stepniak, deputy director of the Polish national archives, at Warsaw airport on Monday.
"We are very, very grateful. These letters are of great value to us," Mr Stepniak told Associated Press news agency.
Dariusz Ganczar, an official from the archives, told the BBC News website: "There are in all 17 letters, all from the 13th Century. Some were written by the Popes Alexander IV and Gregory X, or by high-ranking Roman Catholic Church officials. Others are correspondence between landlords.
Wroclaw is a historic city on the Oder river
"The documents are of great archival and historical value but their content will be disclosed after they have been fully studied, which could take a long time."
The letters are said to be remarkably preserved, with Latin words still legible on the vellum (animal skin).
The Roman Catholic archdiocese of Milwaukee had the documents authenticated in 2003.
After his father's death, Philip Gavin entrusted the letters to the Milwaukee archdiocese, but then he decided to return them to Poland.
Mr Gavin said his father had found the documents in the mud by a burned-out train in Austria.
One possibility is that they were lost during transportation after the Germans fled before the advancing Red Army.