Mourners sing outside the home of former South African President Nelson Mandela in Johannesburg on Monday, December 9. The revered statesman, who emerged from prison to lead South Africa out of apartheid, died on Thursday, December 5. Mandela was 95. 
A groundskeeper collects flowers left by visitors at Mandela's home in Johannesburg on December 9. 
A child checks out at a sculpture of Mandela by Marco Cianfanelli near Howick, South Africa, on December 9. 
A mourner prays on a hill overlooking Johannesburg on Sunday, December 8. 
Young choir members attend a morning Mass on December 8 in memory of Mandela at the Regina Mundi Catholic Church, one of the focal points of the anti-apartheid struggle, in the Soweto district of Johannesburg. South Africans flocked to houses of worship for a national day of prayer and reflection to honor Mandela. 
A South African flag flies at half-staff to honor Mandela on December 8 at the South African High Commission in London's Trafalgar Square. 
A choir sings hymns during a special service in the honor of Mandela on December 8 at the Holy Family Church in the West Bank city of Ramallah. Palestinians mourned Mandela as a loyal champion of their cause. 
Doves are released for Mandela at the Grand Parade in Cape Town, South Africa, on December 8. 
A program is illuminated by the morning sunlight during a service held to honor Mandela on December 8 at First African Methodist Episcopal Church in Los Angeles. 
Areva Martin sings during the service at First A.M.E. Church on December 8. 
A portrait of Mandela is projected onto city hall in Paris on December 8. 
Children in a drum majors group perform a dance outside Mandela's old house on Saturday, December 7. 
Mourners gather in front of the South African embassy in Tehran, Iran, to pay their respects on December 7. 
Crowds of people pay tribute to Mandela outside his Johannesburg home on December 7. 
Christians mourning the loss of Mandela say prayers on a hilltop overlooking Johannesburg on December 7. 
A woman prays at the Central Methodist Church as people remember Mandela on Friday, December 6, in Cape Town, South Africa. 
The South African flag is flown at half-staff at the Union Buildings on December 6 in Pretoria, South Africa. 
Delegates from countries all over the world stand for a moment of silence for Mandela on December 6 during the drawing ceremony for the 2014 World Cup in Costa do Sauipe, Brazil. 
Mandela is honored at the the Grammy Nominations concert at the Nokia Theatre in Los Angeles on December 6. 
A woman cleans up outside the South African Embassy in Beijing where portraits of Mandela and flowers offered by people are placed on December 6. 
European Union flags fly at half-staff at the European Commission headquarters in Brussels, Belgium, on December 6. 
Newspapers with Mandela on the front page are on sale in London on December 6. 
Early morning commuters stand in silence beside a statue of Mandela on December 6 in Parliament Square in London. 
British Prime Minister David Cameron signs the book of condolence at the South African Embassy in central London following the announcement of Mandela's death. 
U.S. Vice President Joe Biden pays a silent tribute to Mandela before his speech on December 6 at Yonsei University in Seoul, South Korea. 
An American flag flies at half-staff above the White House in Washington on December 6. 
Australian and English cricket fans in Adelaide, Australia, observe a minute of silence December 6, to mark the passing of Nelson Mandela. 
A woman cries outside Mandela's house in Johannesburg after Mandela's death on Thursday, December 5. 
South Africans sing as they pay tribute to Mandela in Johannesburg on December 5. 
U.S. President Barack Obama pauses as he speaks about Mandela in the briefing room of the White House on Thursday, December 5. Obama said he was one of the "countless millions" who drew inspirations from Mandela's life. 
The marquee at New York's Apollo Theater honors Mandela on December 5. 
An artist who goes by the name Franco the Great stands beneath a Mandela mural that he painted in New York's Harlem neighborhood more than 15 years ago. He later added Obama to the mural. 
Keaton Anderson, 10, poses for a photograph while he and his father visit Mandela's statue at the South African Embassy in Washington on December 5. The statue is under renovation. 
South Africans pay tribute to Mandela in Johannesburg following his death December 5. 
A candlelight vigil is held December 5 outside Mandela's Johannesburg home. 
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- Elite troops, snipers, canines helping secure stadium
- Government minister says security is in place for Tuesday's memorial
- A state funeral will take place Sunday
- Mandela aide describes sadness and celebration among friends and relatives in his home
Editor's note: Watch the Nelson Mandela memorial from 4 a.m. to 8 a.m. ET Tuesday on CNN International. Dozens of heads of state, including Presidents Zuma, Obama and Castro, will be there with thousands of South Africans at the 90,000 seat FNB Stadium in Johannesburg.
Johannesburg (CNN) -- It's a moment for the ages.
Tens of thousands of South Africans, dozens of presidents and prime ministers, celebrities and street sweepers are all heading to the same place: a stadium in Johannesburg, where they'll honor Nelson Mandela at a memorial service on Tuesday.
With 91 heads of state attending, security will be tight.
Authorities are already stepping up surveillance as presidents of six nations prepare to pay tribute to the late anti-apartheid leader in a four-hour service that will likely bring much of South Africa to a stop.
Nelson Mandela, the prisoner-turned-president who reconciled South Africa after the end of apartheid, died on Thursday, December 5, according to the country's president, Jacob Zuma. Mandela was 95. 
Mandela became president of the African National Congress Youth League in 1951. 
Mandela poses for a photo, circa 1950. 
Mandela poses in boxing gloves in 1952. 
Mandela in the office of Mandela & Tambo, a law practice set up in Johannesburg by Mandela and Oliver Tambo to provide free or affordable legal representation to black South Africans. 
From left: Patrick Molaoa, Robert Resha and Mandela walk to the courtroom for their treason trial in Johannesburg. 
Mandela married his second wife, social worker Winnie Madikizela, in 1958. At the time, he was an active member of the African National Congress and had begun his lifelong commitment to ending segregation in South Africa. 
Nelson and Winnie Mandela raise their fists to salute a cheering crowd upon his 1990 release from Victor Verster Prison. He was still as upright and proud, he would say, as the day he walked into prison 27 years before. 
A jubilant South African holds up a newspaper announcing Mandela's release from prison at an ANC rally in Soweto on February 11, 1990. Two days later, more than 100,000 people attended a rally celebrating his release from jail. 
Mandela and Zambian President Kenneth Kaunda arrive at an ANC rally on March 3, 1990, in Lusaka, Zambia. Mandela was elected president of the ANC the next year. 
After his release in 1990, Mandela embarked on a world tour, meeting U.S. President George H.W. Bush at the White House in June. 
At his Soweto home on July 18, 1990, Mandela blows out the candles on his 72nd birthday cake. It was the first birthday he celebrated as a free man since the 1960s. 
Mandela and his wife react to supporters during a visit to Brazil at the governor's palace in Rio De Janeiro, on August 1, 1991. 
South African President Frederik de Klerk, right, and Mandela shared a Nobel Peace Prize in 1993 for their work to secure a peaceful transition from apartheid rule. 
Mandela votes for the first time in his life on March 26, 1994. 
On April 27, 1994, a long line of people snake toward a polling station in the black township of Soweto outside of Johannesburg in the nation's first all-race elections. 
Mandela in Mmabatho for an election rally on March 15, 1994. 
Mandela was elected president in the first open election in South African history on April 29, 1994. He's pictured here taking the oath at his inauguration in May, becoming the nation's first black president. 
Mandela, left, cheers as Springbok Rugby captain Francois Pienaar holds the Webb Ellis trophy high after winning the World Cup Rugby Championship in Johannesburg on June 24, 1995. 
After one term as president, Mandela stepped down. Thabo Mvuyelwa Mbeki, at right, was sworn in as his replacement in June 1999. 
Mandela sits outside his former prison cell on Robben Island on November 28, 2003, ahead of his AIDS benefit concert at Green Point Stadium in Cape Town. He was sent to the infamous prison five miles off the coast of South Africa, where he spent 18 of his 27 years behind bars. 
Mandela shows something to a group of international journalists visiting the Nelson Mandela Foundation in Johannesburg in May 2004. 
Mandela sits with his wife, Graca Machel, and his grandchildren at his son's funeral on January 15, 2005. He disclosed that his son, Makgatho Lewanika Mandela, had died of AIDS and said the disease should be given publicity so people would stop viewing it as extraordinary. 
The "46664 Arctic" benefit concert was held in Tromso, Norway, on June 11, 2005. 46664 was Mandela's identification number in prison. Here, artists who performed at the event surround him. 
Mandela attends an HIV/AIDs concert in Johannesburg on February 17, 2005. 
Former U.S. President Bill Clinton leans down to whisper to former South African President Nelson Mandela during a visit to the Nelson Mandela Foundation on July 19, 2007, in Johannesburg. 
A bronze statue of Mandela was unveiled in Parliament Square in London on August 29, 2007. The 9-foot statue faces the Houses of Parliament. 
Mandela leaves the InterContinental Hotel after a photoshoot with celebrity photographer Terry O'Neil on June 26, 2008, in London. 
Mandela meets in 2009 with international children as part of his 46664 Foundation. 
Nelson Mandela and his third wife, Graca Machel, arrive at the 2010 World Cup before the final match between Netherlands and Spain on July 11, 2010, at Soccer City Stadium in Soweto. 
Then-U.S. Secretary of State Hillary Clinton meets with Mandela at his home in Qunu, South Africa, on August 6, 2012. 
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The evolution of Nelson Mandela 
Mandela funeral poses security concerns 
Planning for the Mandela memorial service 
Bono: Mandela chose love over hate Working off plans developed for years in secret, the South African government is using an elite military task force, sniper teams and canine teams to help secure the stadium, CNN's Arwa Damon reported Monday. In addition, helicopters and military jets frequently fly overhead.
"Should anybody, anything dare to disturb or disrupt this period of mourning and finally taking and accompanying the former president to his last resting place, then that person will be dealt with," Brig. Gen. Xolani Mabanga said Monday.
South African officials won't give details about their security plans -- how many police officers, how many troops, precautions to keep the stadium weapons- and explosives-free.
"But we can assure that all necessary steps have been taken, and that is why the leadership of the world and former leaders of the world have confidence to come to our country at this time to share with us this moment," said Minister in the Presidency Collins Chabane.
The event promises to rival other significant state funerals in recent decades, such as that of former British Prime Minister Winston Churchill in 1965 and the 2008 funeral of Pope John Paul II, which attracted some 2 million people to Rome -- among them four kings, five queens, at least 70 presidents and prime ministers and the leaders of 14 other faiths.
At that event, metal detectors and some 15,000 members of security forces stood watch over the event.
U.S. official: South Africa experienced at hosting crowds
U.S. officials are satisfied with security arrangements.
"We have not heard any concerns," Deputy National Security Adviser Ben Rhodes told reporters aboard Air Force One as President Barack Obama flew to South Africa.
"The South Africans hosted the World Cup, so they have experience hosting significant crowds and managing events like this, although clearly this is really a unique event in world history, given the number of leaders coming to pay their respects, as well as the people of South Africa."
Given Mandela's ailing health, the U.S. Secret Service made some arrangements in advance, a Secret Service spokesman said. But work that would usually take months to complete has been done in less than a week, the spokesman said.
"It's a compressed timeline, but there are certain protocols we must have in place for any trip," the spokesman said.
Those protocols involve securing the president's motorcade route and hotel rooms and doing security walk-throughs.
The spokesman declined to offer specific details on security measures at the stadium.
While Tuesday's memorial is the first major event honoring Mandela since his death, it won't be the last.
A state funeral will be held Sunday in Mandela's ancestral hometown of Qunu in South Africa's Eastern Cape province.
Four presidents head to Mandela funeral 
Mandela memorial security preps 
Mandela through the years 
How Mandela shaped a new South Africa Presidents set to speak at service
Among the speakers at Tuesday's memorial will be President Obama, who like Mandela was his nation's first black president. Obama has cited Mandela as his own inspiration for entering politics.
In addition to Obama, former Presidents Jimmy Carter, George W. Bush and Bill Clinton will attend. More than two dozen U.S. lawmakers also plan to go.
Other guests include the Prince of Wales, British Prime Minister David Cameron and U.N. Secretary-General Ban Ki-moon, who will also speak, as well as celebrities such as Bono, Oprah Winfrey and Naomi Campbell.
Crews worked overtime Monday to prepare FNB Stadium in Johannesburg for the service.
The stadium, where Mandela delivered his first major speech after his release from prison, can hold some 90,000 people, but that won't be enough to hold the hundreds of thousands clamoring to celebrate Mandela's life.
The government has set up overflow locations at stadiums and other facilities throughout the country.
With private vehicles banned from the area around the stadium, the government pressed buses from around the country into service and stepped up train service to move the crowds.
In addition to Obama and Ban, the presidents of Brazil, Namibia, India, Cuba and South Africa are expected to speak at the service, as are family members, friends and others.
One potential complication: Forecasters predicted potentially heavy rainfall during the event at the open-air stadium.
Monday events
South Africa's Parliament reconvened Monday for an afternoon of speeches and memorials to Mandela. Dozens of members of parliament spoke.
"The world over, his name has evolved into a metaphor," Deputy President Kgalema Motlanthe said. "The name Nelson Mandela has entered the pantheon of history's sages."
Out of the public eye, friends who had not seen each other in years have been coming together with Mandela's family in his home, said Zelda la Grange, Mandela's longtime personal assistant.
Mandela called la Grange his "rock," even though she seemed an unlikely confidante. She was a white Afrikaner and an employee of the former apartheid government.
In her first interview since Mandela's death, she described the mood in his home to CNN's Robyn Curnow on Monday.
"Obviously there's sadness in the house," she said, but also, "People are celebrating Madiba's life. They are grateful." She referred to Mandela by his well-known clan name.
READ: Nelson Mandela's death sparks global response
READ: Prayers, songs for Nelson Mandela at services in South Africa
CNN's Athena Jones, Holly Yan, Chris Cuomo, Kim Norgaard, Robin Curnow, Arwa Damon and David McKenzie contributed to this report.
