  Because of Euler buckling, a simple strut of length $L$ and Young modulus $Y$
requires a volume of material proportional to $L^3 f^{1/2}$ in order to support
a compressive force $F$, where $f=F/YL^2$ and $f\ll 1$. By taking into account
both Euler and local buckling, we provide a hierarchical design for such a
strut consisting of intersecting curved shells, which requires a volume of
material proportional to the much smaller quantity $L^3 f\exp[2\sqrt{(\ln
3)(\ln f^{-1})}]$.
