A modular bridge is formed from a plurality of bridge modules. In one embodiment, the bridge includes: a first longitudinal compression member that is, in use, at an upper part of the bridge cross-section; a second longitudinal compression member that is, in use, at a lower part of the bridge cross-section; a structural lateral element for forming a deck of the bridge or for supporting deck elements of the bridge; a shear element for carrying a shear load; and a tension member applying a compressive force to one of the longitudinal compression members such that when in use the other of the longitudinal compression members forms a main compression element for the bridge and the tension member forms a main tension element for the bridge. The bridge modules form segments of the length of the bridge and each bridge module is of a one-piece construction.