English summary: Although the historic sagas are more well-known, medieval Scandinavians also produced a rich tradition of legendary sagas that recreated their ancient past. These fornaldarsogur are examined in this book, shedding light on this para-religious universe, on its gods, myths, and beliefs from the time before the Vikings. French description: Les sagas islandaises (XIIIe et XIVe siecles) ne forment pas un tout homogene...