German Chancellor Angela Merkel will on Wednesday inaugurate a sombre memorial to the estimated half million Roma and Sinti murdered by the Nazis, joined by survivors of the genocidal campaign.

The long-delayed monument, consisting of a round pool of water and stele on which a single fresh flower will rest each day, sits opposite the Reichstag parliament building in central Berlin.

A timeline of the Nazi extermination drive stands next to the memorial, which was finally built with a federal government grant of 2.8 million euros ($3.6 million).

"Auschwitz" by Italian poet Santino Spinelli is engraved around the rim of the dark pool in English and German, recounting the suffering and sorrow inflicted on the Roma.

It was designed by Israeli artist Dani Karavan, 81, and is located near two other memorials for victims of Nazi barbarism, a sprawling field of pillars for the six million murdered Jews and a smaller monument for gay victims.

Merkel stressed the crucial importance of living up to the crimes of history and providing a site to educate, to mourn the victims and to warn coming generations.

"That is why we must have appropriate places where that is possible -- where people can also go in the future when the survivors are no longer alive," she said in her weekly video podcast.

She will be joined at the opening by President Joachim Gauck and about 100 elderly survivors, as well as the leader of the Central Council of Sinti and Roma in Germany, Romani Rose, who heads a community of about 70,000.

The Nazis deemed the Roma and related Sinti like the Jews to be racially inferior, and unleashed a systematic campaign of oppression against them.

In 1938 SS chief Heinrich Himmler ordered the "final solution of the gypsy question".

Those caught in the sweep were confined to ghettos, deported to concentration camps and slaughtered. Many were subjected to grotesque medical experiments.

Historians estimate nearly 500,000 Roma men, women and children across Europe were killed between 1933 and 1945, decimating a population with roots in Germany dating back six centuries.

Rose, who was born in 1946, one year after the war's end, had fiercely objected to the memorial referring to "gypsies", a term commonly used in the past but now viewed as derogatory.

He lamented that it had taken the West German government until 1982 to acknowledge the genocide but told AFP he was confident the monument would contribute to a gradual ebb in the hatred and bias still faced by Roma today.

"Opening the memorial sends an important message to society that anti-Roma sentiment is as unacceptable as anti-Semitism," he said, adding that the genocide against his people was often seen as a "footnote to the Shoah".

The government's decision to erect the monument dates from 1992 but its opening was held up by bitter rows over its design, cost and inscription.

Some 11 million Roma live in Europe, seven million of them in the European Union, making them the continent's biggest ethnic minority. But they suffer from disproportionate poverty and rampant discrimination.

The fall of the Berlin Wall in 1989 sent many fleeing southeastern Europe for the richer west and countries such as France and Italy have in recent years cracked down on illegal camps.

And Germany recently indicated it would like to curb the flow of Roma into the country, possibly by reinstating visa requirements for Serbia and Macedonia.

[Image via Agence France-Presse]