It extends 24,000 miles, farther and longer than any other measure on earth. Yet the equator is a wholly imaginary construct, a human idea that has fascinated and challenged explorers for three thousand years—from the ancient Egyptian spice traders in search of the legendary land of Punt, to the fifteenth-century Portuguese who sought a route to the Indies, to the expeditions of Victorian naturalist Charles Darwin in the Galapagos Islands, off the Pacific coast of South America, at latitude zero. The equator—its location not only on the globe but also in the minds and exploits of navigators, travelers, poets, and dreamers since the dawn of civilization—is the magical thread on which the eminent Italian historian Gianni Guadalupi strings some of humankind's most intriguing lore and most amazing adventures in this original and riveting intellectual history. The mysterious source of the Nile and the enigma of the Congo's swell, the perils of the Doldrums ("the living death in life" in Coleridge's phrase) and the vicissitudes of El Nino, the quest for the lost Eden and the search for Eldorado, all fall within the compass of Guadalupi's extraordinary volume. So do the names of Columbus, Magellan, Don Lope de Aguirre, Sinbad the Sailor, Henry Stanley, Charles-Marie de la Condamine, and Dante Alighieri, who placed Purgatory on an island athwart the equator.