In this paper, a novel crawler mechanism for sideways motion is presented. The crawler mechanism is of circular cross-section and has active rolling axes at the center of the circles. Conventional crawler mechanisms can support massive loads, but cannot produce sideways motion. Additionally, previous crawler edges sink undesirably on soft ground, particularly when the vehicle body is subject to a sideways tilt. The proposed design solves these drawbacks by adopting a circular cross-section crawler. A prototype has been developed to illustrate the concept. Motion experiments confirm the novel properties of this mechanism: sideways motion and robustness against edge-sink. Motion experiments, with a test vehicle are also presented.