After prising open the entrances to their magnificent stone-walled tombs, they remove the bodies of their loved ones and wrap them in a fresh burial shroud in a ritual called the Famadihana - the "turning of the dead".
Respect for ancestors and beliefs that their souls still influence the world of the living are paramount on the vast Indian Ocean island - but those who do not share this view have decided to make themselves heard.
At a Famadihana in Mahatsara village, 80km from the capital Antananarivo, 200 people turn up to pay their respects on a near-freezing winter morning, unaware the ceremony
will shortly be upset.
"The ritual is always done in winter," said Jahnahary Lahy, 22.
"Winter is when the ancestors need re-wrapping to protect them from cold."
After feasting on roasted pork and beef, mountains of rice and plastic cups of fiery local rum, the guests head for the ancestral tomb.
Colourfully clad musicians play mesmerising flute music as the villagers wind up through the steep, eucalyptus-covered hillsides towards the burial site.
Merina people pay their respects
to ancestors on a chilly morning
Perched on the tomb in a hilltop clearing, village elders open the ceremony with long speeches in deference to the ancestors. Then the dead-turning begins.
Semi-mummified bodies in tatty shrouds are removed from the tomb one by one as groups of villagers take turns to wrap them in fresh white sheets.
Once wrapped, a man pens the name of the ancestor in blue ink on the sheet.
But the mood suddenly changes as one man stands up, clutching a black, leather Bible.
"The ancestors don't exist," he shouts. "You have to forget about ancestors and think about Jesus Christ. He is your true saviour, not these ancestral spirits."
Mouths drop open with shock, and disappointed villagers start muttering under their breath at the interference of the Christian priest, invited to the ceremony by a Christian relative who is sceptical of the whole ritual.
"The organisers are Christian extremists from the town," said one guest, Hery Andrianarivelo, 21. "It's because they had money to pay for this event. They're using it to (try to) change our beliefs."
Ever since Welsh missionaries brought the Bible to Madagascar in the 19th century, tensions have grown between the island's age-old traditions and Christianity - the religion of two fifths of its 17 million people.
About 10% are Muslim, most of the rest hold traditional beliefs.
Unique culture mix
Madagascar is home to a unique mix of cultures that has long fascinated anthropologists.
Waves of immigrants - starting with sea-faring peoples from present-day Indonesia to more recent arrivals from East Africa - have all left their mark.
Anthropologists think the Merina, of all Madagascar's tribes, are the most direct descendants of the Indonesians, and that the practice of exhuming ancestors comes from their forefathers.
In his book on the Merina, From Blessing to Violence (1986), anthropologist Maurice Bloch wrote that "as far as ordinary Merina are concerned, there is little conflict between Famadihana and Christianity.
"The Famadihana does not imply any clear belief in ancestral spirits. It deals with a world of experience, emotion and beliefs that does not seem to ... compete with (those) of Christianity"
"The Famadihana does not imply any clear belief in ancestral spirits. It deals with a world of experience, emotion and beliefs that does not seem to ... compete with (those) of Christianity."
But Elson Randrianasiranana, the Christian Merina who organised this Famadihana, disagrees. He paid the priest to denounce ancestral beliefs in front of his own family.
"Most Malagasy believe in ancestral spirits," he said. "But I no longer believe this. I believe in God now."
Randrianasiranana said he wanted to perform this ritual one last time, but only to show his relatives that good Christians should reject ancestral worship.
"For us, this is our last one," he said. "Christians shouldn't believe in this. From now on, our ancestors are going to stay where they are buried."
Other Madagascans think church-goers who reject their traditions are being unduly po-faced.
"Unfortunately, the Christians sometimes want to spoil the party," said 72-year-old devout Catholic and retired doctor, Martha Razafindrahava. "But why? Why can't we worship Christ and sacrifice a cow to the ancestors at the same time?"
Razafindrahava said Christianity - all sects are well represented on the island - and traditional beliefs are not so different.
"Some Christians think beliefs in ancestral spirits are superstitious," she said. "But we believe in the Holy Spirit. We think a piece of bread can transform into the body of Christ - that's superstition."