More than two decades after Nelson Mandela’s memoir, “Long Walk to Freedom,” became an international bestseller, the late South African president’s prison letters will be published in a volume by Liveright, the publisher announced Wednesday.

Mandela, who died in 2013, was imprisoned for 27 years by the South African regime and became a worldwide symbol of resistance against apartheid, the system of racial laws that oppressed blacks in that country. During that time, Mandela wrote hundreds of letters to family, friends, prison authorities, government officials and others.

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A one-volume edition containing 250 letters will be released in July 2018 to mark the centenary of Mandela’s birth. A larger, two-volume selection of letters will follow at a later date. The books will be edited by Sahm Venter, a former Associated Press reporter who covered Mandela’s release from prison in 1990.

“This collection of letters reminds us of the exceptional pressures on Nelson Mandela to succumb to a system which aimed to wipe him from the public consciousness and which expected him to die a prisoner,” Venter said in a statement released by Liveright. “His resilience and his determination, in the face of enormous odds, to maintain his dignity and authority throughout are apparent in this rich firsthand account of his life in prison.”

Mandela received the Nobel Peace Prize in 1993, and was the first democratically elected black president of South Africa from 1994 to 1999.

A 2013 book, “Conversations with Myself,” contained excerpts from Mandela’s journals, letters, recorded conversations and other materials released from his archives.