BERLIN (AP) — A panel of German and Polish experts on Wednesday started discussing what shape a memorial in Berlin to the Polish victims of World War II should take, embarking on a project mandated last year by the German parliament.

In a resolution approved by most parties in October, parliament called on the German government to “create a place in a prominent location in Berlin that, in the context of the special German-Polish relationship, is dedicated to the Polish victims of World War II and the Nazi occupation of Poland.”

It is also supposed to be a forward-looking concept that aims to “bring together Germans and Poles and so contribute to understanding and friendship, and to breaking down prejudices.”

Nazi Germany invaded Poland in 1939 and subjected its population to more than five years of brutal occupation. Around 3 million of the country’s 3.3 million Jews were murdered, as were more than 2 million other mostly Christian Poles.

That history has been a frequent source of tension between Germany and Poland.

The expert commission aims to produce a concept for the Berlin memorial this summer. It will follow memorials already constructed in the German capital over the past two decades to the Jews, gays, Sinti and Roma and disabled people murdered by the Nazis.

German Foreign Minister Heiko Maas, who opened Wednesday’s meeting, said that “while the Holocaust as the darkest chapter of German history rightly takes the central place in our memory, there are still gaps elsewhere.”

“Those include the particular suffering of the Polish civilian population in World War II,” Maas said in comments released by his ministry. “The madness of the racially ideological war of destruction in eastern Europe started in Poland. Poland was supposed to be erased from the map forever with the destruction of whole cities, mass shootings and resettlement.”