A vertical-motion vibration isolator utilizes negative-stiffness-producing mechanism which includes a plurality of compressed flexures, each having a particular length in the compressed direction of the flexure and being oriented in a horizontal direction, wherein the plurality of compressed flexures are positioned relative to each other such that the length of each compressed flexure substantially overlaps the length of each of the other compressed flexures. At least some of the plurality of compressed flexures can be positioned in a stacked arrangement. The arrangement of compressed flexures forming a portion of the negative-stiffness mechanism can reduce the size of the isolator without compromising vibration isolation performance.