Celebrations are being held to mark 20 years since the release from prison of Nelson Mandela, a key step towards ending apartheid in South Africa. In Cape Town, prominent figures took part in a commemorative march from the prison where he spent the final months of his 27-year imprisonment. Mr Mandela, now a frail 91-year-old, is expected to make a rare public appearance on Thursday evening. He became the country's first black president in 1994. He was sentenced to life imprisonment in 1964 for plotting to overthrow the government by violence. He spent most of his sentence in Robben Island prison, off the coast of Cape Town, and later in Pollsmoor Prison on the mainland. Before his release, he lived in a cottage in the grounds of Victor Verster prison in a rural area some 50km (31 miles) from Cape Town, with his own cook. Thursday's re-enactment walk was from Victor Verster prison, now known as Drakenstein Prison, where a statue of Mr Mandela stands with its hand upraised. His former wife, Winnnie Mandela, had been due to lead the march, but a spokesman said on Thursday morning that she would not be appearing because it would have been "too painful". Mr Mandela was not taking part, but he is expected to attend a state of the nation address by South African President Jacob Zuma later. International pressure During his years in prison he became an international symbol of resistance to apartheid. In 1990, the South African government responded to internal and international pressure and released Mr Mandela, at the same time lifting the ban against the ANC. Cyril Ramaphosa, head of the committee that had to protect Mr Mandela in the days after his release, said the country had undergone enormous changes in the last two decades. "If you cast your mind to 20 years ago, could we ever have imagined that we would be where we are today. "Not many of us could have imagined this. "We possibly do remember where each one of us was when Nelson Mandela walked free, but I don't think many of us could ever have imagined that we would be living in a South Africa that resembles what it is today." 'Good solution' Christo Brand, the former prison warden assigned to guard Mr Mandela, said of events 20 years ago: "I hoped there would be no bloodshed. There was no bloodshed. Everything worked out perfectly. "And I know the way Mandela does negotiations, he was really thinking of the other side, too. "He not only thinks of the black people of the country, but thinking also of the whites and studying and feeling the fears of the whites in this country. "And I think through that fear, he came up and thought of a good solution for South Africa." In 1991 Mr Mandela became the ANC's leader, and was president of South Africa from 1994 to 1999. Source: BBC