In the year of the one hundred and seventy-seventh Olympiad (70 B.C.), Posidonius of Apamea, a famous Rhodian philosopher who had devoted his life to the search for knowledge, finally fulfills an ancient longing: to travel to Gadir, the mythical Canaanite city of distant west, to visit the famous temple of Melqart. Thanks to the influence of his protector, Pompey the Great, Posidonius obtains the rare privilege of staying in the temple itself, where he wants to observe the stars, study the tides and consult the funds of his extraordinary library. Without knowing it, the Greek gets into the mouth of a volcano about to explode. His presence in Gadir arouses the misgivings of the supporters of the old order, who are reluctant to renounce their traditions, despite the pressure exerted by the Romans as the new masters of the world. Human sacrifices, ritual prostitution or the death penalty for criminals, arouse fierce conflicts between the reformers, led by the Balbo family, and the conservatives, led by the priestly caste. Tireless seeker of the truth behind every challenge, Posidonio has always followed the voice of reason. But it is in the West that he faces, for the first time, the moral dilemma of his commitment. In Gadir, everything changes for him.