Abstract: A container of generally rectangular shape is formed with a self-locking bottom wall from a single blank of cut and scored fiberboard material. A pair of bottom panels fold inwardly and upwardly from the bottom edges of one pair of side walls to form the bottom of the container; and a pair of reinforcing panels simultaneously fold inwardly to upright, strengthening positions against the inside faces of the other pair of side walls. The interconnected bottom and reinforcing panels are locked in place by hold down flaps folded downwardly from the reinforced side walls over the reinforcing panels.