A structural system and method of assembly comprising structural members with slots, and interior structural members. Specific structural members are sequentially interconnected in rigid alignment. A first structural member is positioned with two upward facing slots. Additional structural members are added by engaging downward facing slots of the additional structure members with upward facing slots of the prior structural member. The structural members further include engagement features in cooperating slots. A protruding features engages a recess to retain the engaged structural members. The features may be a partial sphere and a matching recess which may be disassembly, or a tapered protrusion having a squared-off rear edge which resists disassembly, or one of a variety of shapes.