(pronounced Marbay, often spelled that way). A "shithole". Used to describe either a place or town, or a trench used for depositing faecal matter in the field. Also a particularly foul toilet. A UK armed forces term used by squaddies. Comes from the trenches of world war one, Marbaix being a place on the trench line in Nord pas de Calais where a severe outbreak of dysentery occurred. Hundreds of sick soldiers were forced to shit where they stood in the trenches for months, turning the trench into a literal "shithole".
"just got back from Nad e ali, place is a total Marbaix"
"Jesus those bogs are fucking marbaix"
"You're on Marbaix duty private, get your spade and start digging"