The ability to independently control fiber alignments and structural geometry is critical for design of optimal three-dimensional (3D) fibrous structures. We present a novel method to 3D-assemble carbon fiber structures, containing no seams or adhesive joints, using a confluence of several textile methodologies. A variety of complex structural shapes with tailored fiber topologies are demonstrated to be achievable. These optimized structures are shown to have unprecedented static and dynamic strength as well as damage tolerance and ductility. For example, the energy absorption capacity of a 3D-assembled carbon fiber prismatic sandwich structure is shown to be 300% greater than a high performance metallic counterpart.