Tens of thousands are gathered inside a Johannesburg soccer stadium for a memorial to Nelson Mandela today as millions watch from around the world. Mandela died last week at the age of 95. United Nations Secretary-General Ban Ki-moon was among the speakers to pay tribute. Nearly 100 heads of state traveled to South Africa for the memorial, including President Obama and Cuban President Raúl Castro. In an unprecedented exchange, Obama shook Castro’s hand as he made his way to speak at the podium. Joining Obama in the U.S. delegation are former Presidents George W. Bush, Bill Clinton and Jimmy Carter. Jay Naidoo, a close friend of Mandela’s and one of his first government ministers, told The New York Times he is choosing to watch the memorial from the crowds, saying: “This is a day for the people, not the powerful. What Nelson Mandela stood for most of all was solidarity with the downtrodden of the world, and for them he is a symbol of social justice and human rights. That is why I am saying my goodbye from the ranks of the people.”