In the 1970s, 5 miles off the coast of Cape Town, South Africa, Nelson Mandela and other political prisoners languished in a high-security prison known as Robben Island. They were each allowed a single book, but as political tensions rose on the mainland, guards threatened to take away any nonreligious reading material.

Anti-apartheid activist Sonny Venkatrathnam couldn’t bear the thought of losing his book, the collected works of Shakespeare, so he disguised it with images of Hindu gods and told gullible guards that the tome was his bible. The ploy worked.

“[The wardens] saw this volume with two columns of text and numbered verses … and it looked like a bible to them,” says Caryn Lazzuri, exhibitions manager at the Folger Shakespeare Library.

After spending seven years in prison, Venkatrathnam was released in 1978. Before he left, he asked his fellow prisoners, including Mandela, to sign their names next to passages that were meaningful to them. The so-called “Robben Island Bible” is on display at the Folger, alongside four sketches of Robben Island made by Mandela in the 2000s.

Lazzuri walked us through the show’s elements and their significance.

Above left: Political prisoner Sonny Venkatrathnam covered his copy of the collected works of Shakespeare with Diwali greeting cards sent by his family. The cards, which celebrate the Hindu festival of lights, tricked prison guards into thinking the book was a religious text. “Sonny has said … if it wasn’t for having this book of Shakespeare, he would have gone out of his mind in prison,” due to boredom, Lazzuri says.

Above right: Nelson Mandela signed his name, inset, next to a passage in “Julius Caesar” that begins,“Cowards die many times before their deaths: The valiant never taste of death but once.” For Mandela, it was a statement of resolution by a young man who had already lived a full life devoted to justice, Lazzuri says. But in the context of the play, it’s the self-aggrandizing speech of a nascent tyrant — an irony that Mandela was probably not aware of. “If you are signing your name by a passage you aren’t necessarily considering the full context of play,” she says. “You pull it out like an aphorism.”

In 2002, Mandela began a series of drawings of Robben Island, which were made into lithographs and sold to benefit the Sebastian Hunter Memorial Trust, a charity supporting education and child care initiatives for the rural poor. This sketch depicts a church that became a beacon of hope to many prisoners on Robben Island, even though they were not allowed to enter it. The cheery colors fit with Mandela’s view of the prison as “a symbol of the finest qualities of the human spirit, rather than as a monument to the brutal tyranny and oppression of apartheid,” he wrote in an artist’s statement.

Folger Shakespeare Library, 201 E. Capitol St. SE; through Sept. 29, free; 202-544-4600. (Capitol South)