The present invention relates to a foldable barrier structure comprising a compartment bounded by a pair of opposed side walls and a pair of opposed end walls, at least one pair of opposed side or end walls being formed from a flexible, foldable material incorporating a stiffening element and a means for receiving a hinge member which permits folding of a central region of each opposed side or end wall of the at least one pair of side or end walls. Also provided is a multi-compartmental foldable barrier structure comprising a multiplicity of such compartments connected, affixed or adhered to one another end to end, as well as a flood defense barrier comprising a first multi-compartmental foldable barrier structure provided with a continuous length of water impermeable material extending across the individual structures along at least one side of the barrier; a second multi-compartmental foldable barrier structure provided with a continuous length of water impermeable material extending across the individual structures along at least one side of the barrier; and fastening means for fastening the first multi-compartmental foldable barrier structure to the second multi-compartmental foldable barrier structure.