Syarifa Fatimah Zuhra's eight-year-old son, Muhammad Reza Syahputra, died when the Boxing Day tsunami hit Aceh 10 years ago. His body was never found, so she comes to the children's section of the mass grave in Ulee Lheue to pray.

Caretakers tell us 14,264 unidentified bodies are buried in three layers in this mass grave alone. It's one of eight in the city of Banda Aceh.

Apart from her son, Ms Syarifa lost her husband and most of the rest of her family.

"We don't know where their bodies are but whenever we pray, we hope God will pass on our prayers to them," she says.

A few kilometres away, on Banda Aceh's main park, Blang Padang, which became a vast open-air morgue in the days after the wave, dignitaries from Indonesia and the world gathered to remember. Indonesia's vice-president, Aceh's governor and two dozen ambassadors, including Australia's charge d'affaires, David Engel, came to "contemplate and be thankful", in the words of governor Zaini Abdullah.

Vice-President Jusuf Kalla - who was the deputy to a different president 10 years ago, when the tsunami hit - remembers coming to this field when it was heaped with death. An estimated 167,000 people died in Aceh alone, among at least 230,000 worldwide.

"It was a huge tragedy for humankind," Mr Kalla says, "To bury hundreds of thousands of people is something that is difficult; but rebuilding lives of millions of Acehnese is even more difficult."

He recalls an hour-long meeting in Jakarta at which foreign governments pledged $US5 billion.

Being Aceh, though, the work of both humans and nature are the work of God.

"The tsunami was Allah's test for Aceh and it passed," preacher Syech Ali Jaber told a packed mosque on Christmas night, the eve of the commemoration.

A Koran verse read out the following morning was even more explicit: "Those who deny their faith must expect punishment . . . They reject the verses [of Allah] so Allah torments them."

The idea of the tsunami as punishment reaches deep into society here, even into the families of those who died.

At the mass grave, Dahn Nuraini sits weeping with her family for her beloved older sister. Ms Nuraini's niece also died, though her body was recovered and buried by the family.

"I believe it was a warning because back in those days there were a lot of young couples who had parties or acted freely by the beach," Ms Nuraini says.

Was her sister a sinner?

"When God sends a test, he doesn't just pick the actual sinners. It's random. It shows people that they have to introspect, to be better in the future."

Aceh is physically better than it was, she says, but has slipped even further into moral decline: "When it comes time to pray, people don't immediately leave the cafes."

When Ms Syarifa lost her son, "the sadness was indescribable". Reza was a good boy, "obedient, diligent", she says, and his death brought her close to despair.

In the depths of her mourning, "it felt like Doomsday".

The only thing that got her through was God.

"We surrender everything to God … if we put our faith with God, we will be stronger to survive. If we didn't do that then, we would have been defeated by it."