19 April 1963
On 19 April 1963, African National Congress (ANC) leader Walter Sisulu forfeited R6000 bail and went underground. Security Police visited Sisulu's house and found out that Sisulu had fled. The incident happened while he was awaiting the outcome of an appeal against a 6 year sentence. On the following day it was published in the Rand Daily Mail (a newspaper banned in March 1985) that he fled to Bechuanaland (now known as Botswana). Three Months later, Sisulu and the high command of uMkhonto weSizwe(MK), armed wing of the ANC were arrested at Lilliesleaf Farm in Rivonia during a raid conducted by security police.
References

O’Malley, P. ‘1963’, from O’Malley, [online], Available at www.nelsonmandela.org [Accessed: 15 March 2012]|South African History Online, ‘The Revonia Trial and Lilliesleaf Farm’, [online], Available at www.sahistory.org.za [Accessed: 15 March 2012]