The men had been killed by German soldiers while fighting German rule in what is now Namibia, or had perished of disease in the camps.

The skulls were stripped of soft tissue using boiling water and glass shards. They were then shipped to Germany for scientists to test the racial theories that were popular at the time.

German troops had captured primarily members of the Herero ethnic group, but also some of the Nama. Both had risen against their colonial rulers in a rebellion that was put down with extreme brutality at the start of the 20th century.

Many were killed in the fighting, many more died of hunger and thirst after being driven into the desert, and many of those taken prisoner died in concentration camps as a result of forced labour and disease.

Many of the Herero and Nama skulls are now stored at German museums, universities and research institutes.

Berlin's Charite Hospital is the first institution to hand over its collection to Namibia. Representatives of the Namibian government, the Hereros and the Nama flew to Berlin to witness the formal return on Friday of the skulls.

The Namibian government raised the issue with Berlin three years ago, demanding the return of all the skulls still held in Germany. An investigation at the Charite listed 11 skulls from the Nama group and nine from the Hereros.

A spokeswoman for the Charite, one of Germany's most prestigious university hospitals, said the skulls would be returned to contribute to reconciliation.

"We know today that the anthropologists of the time wronged both the living and the dead," she said.

The Charite collection holds around 7 000 skulls from all over the world, some dating back to Germany's brief colonial period. Others go back even further.

At the time when the collection was made, the discipline of anthropology was in its infancy. "The aim was to collect at least one skull from each ethnic group in the world in order to compare the characteristics," Charite representative Andreas Winkelmann says.

Many of the scientists were looking for a basis for their racial theories. Others believed that many ethnic groups would soon die out and that it was important for science to retain something from them.

How many other skulls in the Charite collection might belong to Namibians is uncertain, according to Winkelmann. He estimates there may still be as many skulls as those identified so far.

Victims' associations in Namibia want certainty, but identifying skulls as belonging to Herero or Nama is difficult.

Ueriuka Festus Tjikuua of the Ovaherero/Ovambanderu - Council for Dialogue on the Genocide of 1904 expressed the anger still felt.

"We have come to demand reparations," he said. "You're giving us the skulls, but where is the flesh?"

A German Foreign Ministry spokesman said the government had repeatedly "acknowledged Germany's moral and historical responsibility to Namibia."

Germany was assuming its responsibilities "through strengthened bilateral cooperation, particularly in the area of development work in Namibia," he said.

In August 2004, the German aid minister at the time, Heidemarie Wieczorek-Zeul, went to Namibia to admit that the Germans of 100 years ago had committed "genocide." She asked Namibia for forgiveness.

Berlin later pledged $27 million in aid to Namibia in 2007 as a form of reparation.