Preparing the biggest homecoming yet of its kind, authorities in New Zealand on Monday received 20 ancestral heads of Maori ethnic people once held in several French museums as a cultural curiosity. French Culture Minister Frederic Mitterrand and New Zealand’s ambassador presided over a solemn ceremony at Quai Branly museum in Paris, where the heads were encased in a box — the largest single handover of Maori heads to be repatriated, New Zealand’s embassy said. Since 2003, the South Pacific country has embarked on an ambitious program of collecting back Maori heads and skeletal remains from museums around the world. Yet the program has run into significant obstacles. France long resisted handing over such cultural artifacts, but a law passed in 2010 paved the way for the return of the Maori heads. They were obtained as long ago as the 19th century, and one as recently as 1999. Some Maori heads, with intricate tattoos, were traditionally kept as trophies from tribal warfare. But once Westerners began offering prized goods in exchange for them, men were in danger of being killed simply for their tattoos, French museum officials have said. The heads handed over to New Zealand were not available for public viewing on Monday. Over the years, French museums, private collectors and anthropological researchers have preserved and stored the heads. The idea behind getting back the body parts was that they would be returned to their home tribes throughout New Zealand, where tribal elders could mourn them and, if they chose, give them proper burials. “They are, after all, human remains, and in the Maori culture they should not be publicly displayed,” said Pou Temara, a university professor who chairs New Zealand’s repatriation advisory panel. Bridget Gee, a New Zealand embassy spokeswoman, said the heads remanded on Monday have not been displayed in public for years. Most of the remains aren’t readily identifiable, and only a small percentage have been returned to their home tribes — who are loath to accept any remains that aren’t their own. Heads and body parts from over 500 people now sit in storage at the national musuem, Te Papa, in Wellington. The practice of preserving heads was begun by Maori as a way of remembering dead ancestors. In the decades after Europeans arrived, the heads became a curiosity and sought-after trade item, prompting Maori to ramp up their production levels.