The 13th Immortal (1957) novel

Robert Silverberg's 1957 novel The 13th Immortal is set in the post-apocalyptic future of the 26th century which followed the Years of the Freeze (2062-2527). On this far future Earth, 12 immortal humans have divided the world into 12 dukedoms. The title refers to the mystery of a 13th immortal human on the Antarctic continent. The 13th Immortal, written when Silverberg was 21 and originally published by Ace, was reissued in 2004 by Dorchester Publishing (New York, NY) in collaboration with Wildside Press under the latter's Cosmos Books imprint (ISBN 0-8439-5951-7).