Carmina Burana is the name of 254 poems and play fragments written in the 11th, 12th, and 13th centuries. They were written by students and clergy, primarily, and consist mostly of songs to sing while walking, campfire songs, drinking songs, comedy songs, love songs, and some love and story-poetry. Many of them satirize the Roman Catholic Church, and a number are pretty bawdy (even erotic). The collection of poems and sons was found in 1803 in the Benedictine monastery of Benediktbeuern, Bavaria.
"O Fortuna" is the opening piece, and describes a person's love-hate affair with the Goddess of Fortune for her fickleness.
The mass choir, the throbbing tempo, minor key, and the ever-rising melody make it a favorite of fantasy film directors -- who find its Latin lyrics very "pagan" and "real."