A structure for example a blast protection structure (1) is provided formed by the inflation of one or more containers (2, 3, 4) and (5) which are then filled with a settable cement or other material to provide a rigid free-standing structure. Roof members (8, 9, 10, 11 and 12) (FIGS. 2 and 3) may be provided also. The roof is formed by inflating roof supports (8, 9) and (10), forming a further roof member (11) from settable cement material above the roof supports (8, 9) and (10), deflating the roof supports (8, 9) and (10) when the further roof member (11) has set to leave the further roof member (11) in place and forming a structural roof member (12) above the roof member (11). The containers and/or inflatable supports may be formed from dropstitch material which provides internal reinforcing. The invention allows free-standing rigid structures to be produced without the need for conventional formwork. Thus, inflating equipment and means for pouring cement etc into the containers and supports is the only equipment required for the erection procedure.