The film begins by explaining how tree- rings can be used as a dating tool (dendrochronology), in temperate climates where annual age- rings can be found. Synchronization allows us to determine the year, even season, of the felling of the tree, whose wood was used to make the artifacts we want to date (e.g. stakes, beams, shipwrecks, pieces of furniture, statues, boards). This method has been succesfully used in Europe for nearly forty years. The film shows the various stages of the operation: taking samples on the ground, technical operations in the workshop and laboratory analysis. The dating of a shipwreck discovered in the Rhone river- bed, at Arles, and its interpretation illustrates the contribution of this dating method to the archaeology of the ancient Mediterranean.