I nominate Memoirs of Hadrian by Margeurite Yourcenar, originally written in French. I've wanted to read this for awhile now; it was nominated and ended only one vote away from winning in the other club some years ago.
From Goodreads:
Both an exploration of character and a reflection on the meaning of history, Memoirs of Hadrian has received international acclaim since its first publication in France in 1951. In it, Marguerite Yourcenar reimagines the Emperor Hadrian's arduous boyhood, his triumphs and reversals, and finally, as emperor, his gradual reordering of a war-torn world, writing with the imaginative insight of a great writer of the twentieth century while crafting a prose style as elegant and precise as those of the Latin stylists of Hadrian's own era.
Goodreads