A trapezoidal endless power transmission belt structure is provided which is made primarily of elastomeric material and has a pair of oppositely arranged surfaces disposed in spaced relation to define an outside and inside surface of the belt structure and has a load-carrying section arranged midway between the inside and outside surfaces. The belt structure has a tension section and a compression section which are of similar construction and each is comprised of a plurality of layers including a fiber-loaded layer disposed adjacent the load-carrying section and a fabric layer disposed remote from the load-carrying section; and, the fabric layers and fiber-loaded layers cooperate to assure that the belt structure has longitudinal flexibility yet has transverse rigidity or stiffness sufficient to enable the belt structure to be operated in associated sheaves free of shear planes parallel to the load-carrying section.