"We just want to know what happened to them... we want a grave where we can leave flowers," Wadad Halawani, president of the Committee of the Families of the Kidnapped and Disappeared, told AFP.
The civil war lasted 15 bloody years from 1975 to 1990, killing more than 150,000 people and leaving some 17,000 missing, according to official figures.
The conflict primarily pitted Christian groups against Palestinian factions backed by leftist and Muslim parties, with significant regional and international intervention.
"Those who buried their children were able to weep for them, but we have not been able to mourn," said Mariam Saidi, whose 15-year-old son Maher disappeared in 1982 while fighting near Beirut.
"It's a cause that must not die," she insisted in her apartment on the old line that separated largely Christian east Beirut from the mostly Muslim west of the city.
Like the Argentine Mothers of the Plaza de Mayo movement, Saidi has since 2005 participated in a permanent protest camp outside the UN headquarters in central Beirut.
But despite the long-running protest and various campaigns, the parties to the civil war have refused to share information about the missing.
"They refuse to reopen the files, saying it will threaten civil peace. As if the country was at peace!" Halawani said.
Lebanon has experienced many spasms of violence since the war, and has been criticised by international NGOs for its "collective amnesia" about the conflict.
'We want the truth'
"To learn the lessons of the war, the past must be confronted," said Carmen Hassoun Abu Jaoude, director of the International Centre for Transitional Justice (ICTJ) in Beirut.
"It's a wound that was closed up while it was still infected," she added, noting that investigations into the fate of the disappeared in other countries had not rekindled conflict.
In 1991, Lebanon issued a broad amnesty that benefited the country's warlords, allowing many of them to become political leaders.
"Abroad, people are astonished when I tell them we don't want justice or the cancellation of the amnesty law," said Halawani, whose husband was kidnapped in front of her in 1982.
"We cannot put all the political leaders in jail. We just want to know the truth and reconcile with the past."
Under pressure from relatives, Lebanon's government in 2000 acknowledged the existence of mass graves in the capital, without beginning any identification efforts.
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And last year, the country's highest judicial body ruled that the families had the right to know the fate of their loved ones.
However, little progress has been made.
Since 2012, the International Committee of the Red Cross has been compiling a database of information about each disappeared person.
Fabrizio Carboni, ICRC Lebanon president, said efforts were under way to get approval from the authorities to collect saliva samples from still living parents of the disappeared for future DNA analysis.
The ICTJ has drafted a law, which would have to be approved by parliament, that would create a commission of inquiry into the issue, led by the police and aided by specialised archaeologists and anthropologists.
As they fight for information, many relatives of the disappeared struggle to live normally, feeling that time just stopped when their loved ones went missing.
"There's Um Issam, who hasn't left her house for several years, convinced that her son will knock on the door any minute," Halawani said.
Other mothers sit by the window, hoping to see a returning child; or they have left their children's rooms untouched since their disappearance.
Many, like Saidi, have experienced dashed hopes and false promises of a reunion.
"When they would tell me Maher was free, I would start dancing," she said.
"The next day there would be no news, and I would cry and scream his name all night."
Despite her pain, she harbours no desire for vengeance.
"I support the cause of all the mothers of the disappeared, even those whose sons were Lebanese Forces" and fought against Maher.
Among the disappeared are dozens of people who were taken to Syria during the war and in the early 1990s.
Damascus has always denied holding political prisoners, despite the presence of Lebanese detainees in several releases between 1976 and 2000.
Marie Mansourati, 83, is sure that her son Dani is still alive, more than two decades after being taken to Damascus in 1992.
Her hands trembling, she smokes cigarette after cigarette in her Beirut apartment.
"I don't meet people any more -- I have worn black all these years."
"I just want him to come back and call me 'Mum'."