Mandela critical as anniversary marked NELSON Mandela remains in a critical condition in hospital as South Africa marks 50 years since the police raid that led to his life sentence. Visiting Mandela for the second time in 24 hours, President Jacob Zuma said Thursday that the anti-apartheid hero was continuing to respond to treatment, remaining in a critical but stable condition. During Mandela's hospitalisation - his longest since leaving prison in 1990 - South Africans have marked a series of anniversaries of major events in the peace icon's life. Anti-apartheid veterans on Thursday marked half a century since 18 members of Mandela's African National Congress were arrested in a police raid on Liliesleaf farm in Rivonia, near Johannesburg. Mandela was already in custody at the time of the raid, but the documents seized during the swoop allowed authorities to try him again, leading to his 27-year imprisonment. Deputy President Kgalema Motlanthe said Mandela was the only survivor missing from the commemoration, but he was there in spirit. He has always been present in many deliberations and today is no exception... even as we converse here his presence looms large in the background. That's really the measure of the man. Some of Mandela's prison mates also marked the anniversary, with the foundation of Ahmed Kathrada, one of the men arrested during the raid, saying the occasion was "particularly poignant" given Mandela's condition. It was at the Rivonia trial that Mandela gave his famous "I am prepared to die" speech, saying he was prepared to die for the ideal of a democratic and free society. Mandela, who turns 95 next week, was rushed to a Pretoria hospital on June 8 with a recurring lung infection. Doctors are said to have ruled out switching off Mandela's life support machines unless there is serious organ failure.