We prove that an indecomposable principally polarized complex abelian variety $X$ is the Jacobian of a smooth curve if and only if there exist points $a, b, c$of $X$ whose images under the Kummer map $X \rightarrow |2\Theta|^{\ast}$ are distinct and collinear, and such that the subgroup of X generated by $a - b$ and $b - c$ is dense in $X$.