Nine Princes in Amber was the first book in Roger Zelazny's seminal Chronicles of Amber fantasy series, and was first published in 1970. Zelazny melds several elements in this book - immortality of his god-like protagonists, fantastical creatures, a unique brand of magic, as well as detailed swordplay.
Amber is the True World and all other worlds just Shadows of Amber. Amber is ruled by an immortal family which includes nine living brothers, the Princes. Their sisters are also immortal but do not compete for the vacant throne of their father, Oberon, who is apparently not dead but only missing.
The royals can walk from one Shadow world to another by a process of subtraction where the elements that do not belong are removed one at a time until the royal is fully in the new Shadow. They bring armies from one Shadow to Amber in a contest for the throne.
Another interesting plot element is the Trumps, a series of tarot-like cards depicting the royal family. Any prince or princess can communicate directly and teleport through the use of the Trumps. Their use requires the willingness of both royals and they are used both offensively and cooperatively.
As classic fantasy Nine Princes in Amber is strongly recommended. It is interesting to compare the themes and elements of this early classic with current fantasy. For example, two dated plot elements are Corwin's constant smoking of ordinary cigarettes and the relatively minor roles of the princesses.
And today's poem:
Myths and Gods
The storm had passed
Leaving loss and waste
And a darkness, black
Against which stand back
The stars in bright relief.
You feel the Greek belief
In their myths and their gods
Without our technical clods.
Closer to the best of nature
Even in the midst of disaster.
From Transitions by Greg Schroeder.