The first edition of Légendes is a boxed set containing three softcover books.
The first book (64 pages) contains the basic rules, including character creation, combat and magic.
The second book (56 pages), advanced rules, contains a lot of additional details, aiming to create a realistic simulation of day-to-day life in a mythological ancient history setting.
As such, the rules can be used in other settings.
The third book ("civilisation", 104 pages) explains everything there is to know about the Celt civilization circa 200 BC.
My copy of the last book (see image 1768918, although mine is coloured like the box set) has 120 pages and contains 31 pages of history, myth, culture and civilization; the remaining pages detail the rules (character archetypes, weapons, equipment, skills, etc.). ISBN 2-904 783-14-8 Maybe this is a separate edition of the rule set? It is also dated 1985 (copyright 1983).