The song
In Marieke Brel sings about a Flemish girl, Marieke, whom he once loved and lived "between the towers of Bruges and Gent". He wants her to love him again in the "flat country of Flanders" (a reference to another song by him, "Le Plat Pays").
It's also the only song where he sings both in his native French language and in Dutch, the other major language of his bilingual home country Belgium. Brel recorded a version of the song entirely in Dutch, as well, with lyrics by Eric Franssen.
Covers
"Marieke" has been covered numerous times, among others by Marie Bill, Hans de Booij, Donald Cant, Judy Collins, Shawn Elliott, Elly Stone, Mort Shuman, Alice Whitfield, Amanda McBroom, Des de Moor, Barb Jungr, Liza Minnelli, Danièle Pascal, Laurika Rauch, Laïs, Karin Hougard, Klaus Hoffman, Herman van Veen, Evabritt Strandberg, Michael Heltau, Gay Marshall, etc.
Brel told singers who covered "Marieke" that he didn't mind that they changed the French lyrics, but preferred the Dutch lyrics to remain intact.