Abstract: A modular construction system and modular member are provided for the construction of concatenated structures having interconnected, overlapping, offset or parallel courses. The modular members are provided with substantially planar upper and lower surfaces with the thickness, width and hole spacing of each modular member being predetermined and interdependent. The modular members present holes which receive connectors, and may have holes presenting a plurality of bore diameters. The members may be cut perpendicular to the longitudinal axis of the member midway between adjacent holes to provide compatible modular member segments. The complementally shaped connectors are received in the holes and may include mechanical barbs or threads, or separate retainers for use with the connectors inhibit preventing vertical separation of overlapping adjacent modular members.