Helliconia #1: Helliconia Spring by Brian W. Aldiss

A planet orbiting binary suns, Helliconia has a Great Year spanning three millennia of Earth time: cultures are born in spring, flourish in summer, then die with the onset of the generations-long winter.
Helliconia is emerging from its centuries-long winter. The tribes of the equatorial continent emerge from their hiding places and are again able to dispute possession of the planet with the ferocious phagors. In Oldorando, love, trade and coinage are being redisovered,This is the first volume of the Helliconia Trilogy—a monumental saga that goes beyond anything yet created by this master among today’s imaginative writers