The Indonesian government and rebels from the Free Aceh Movement (Gam) have signed a peace deal aimed at ending their nearly 30-year conflict.
The two sides acknowledged there was still a lot to be done
Representatives from each side signed the official document in Helsinki.
"This is the beginning of a new era for Aceh," said former Finnish President Martti Ahtisaari, who mediated the talks. "Much hard work lies ahead."
Efforts to end the conflict resumed after the tsunami in December, which destroyed vast swathes of Aceh.
In the provincial capital, Banda Aceh, big screens were set up in the main mosque so that people could witness the signing.
KEY POINTS OF THE ACCORD
All hostilities cease and Gam disarms
Government withdraws non-local military and police
Aceh to be governed under a new law
Government facilitates Aceh-based political parties
Amnesty granted to Gam members
Truth and reconciliation commission established
Aceh monitoring mission set up by EU and Asean
Locals have also begun two days of prayers in support of the peace process, in the hope that this time it really does signal the start of a new chapter for their beleaguered province.
"I can't predict what will happen now," said local school teacher Nassruddin.
"I only know we want to see an end to the fighting, we want prosperity, and to feel safe," he told the Associated Press.
15,000 people have died in more than 29 years of conflict between the government and the rebels in Aceh.
Terms of the deal
After the two sides had signed the peace deal on Monday, Mr Ahtisaari said: "We are witnessing here today the culmination of a peace process, which led to a memorandum of understanding between the Indonesian government and the Free Aceh Movement."
"We are here to try to make history," said Indonesian Justice and Human Rights Minister Hamid Awaluddin, at the signing ceremony. "Let's not make the bitterness of the past destroy our future."
Malik Mahmud, the head of the Gam delegation, also spoke of a more peaceful Aceh.
In Aceh, people prayed that this time the peace would last
"This peace process has required a leap of faith from Gam," he said. "It is a leap of faith we have taken to give the people of Aceh the opportunity to build a brighter future."
But he added: "It would be naive not to recognise there are many challenges. We know the real hard work remains ahead of us."
Under the agreement, whose details were only released on Monday, the rebels have put to one side their demand for full independence, accepting instead a form of local self-government and the right eventually to establish a political party.
In turn, the Indonesian government has agreed to release political prisoners and offer farmland to former combatants to help them reintegrate into civilian life.
A human rights court will be established, as will a truth and reconciliation commission.
ACEH: ESSENTIAL FACTS
Located on the northern tip of Sumatra island
Population of 4.3m people
Rich fuel resources, including oil and natural gas
Gam rebels have been fighting for an independent state
Non-local Indonesian troops and police will leave Aceh, and Gam revels will disarm, in a process which will be overseen by a joint European Union and Asean monitoring team.
During his speech to mark the signing, Malik Mahmud said that pro-government militias in Aceh must also be disarmed.
"It is difficult to believe police will take arms from them," he said, adding that the international monitoring team will need to ensure this requirement is enforced.
Gam estimates there are 10,000 such militia troops active in Aceh.
The BBC's Jakarta correspondent, Rachel Harvey, says that while the signing of the deal is undoubtedly a step forward, the first real test is likely to come in one month's time, when rebels are supposed to start handing in their weapons.
Previous peace deals have fallen apart and on the ground there is still deep mistrust between the two sides.
But there does now seem to be a real political will to make this agreement work, our correspondent says.