A specialized loom that lifts some of the warp (lengthwise) threads so that the weft (crosswise) threads can be passed through the warp easily and quickly. The heddles are short lengths of wire or flat steel strips used to deflect the warp to either side of the main sheet of fabric. Originally heddles were movable rods, but later cords, wires, or steel bands were used. They are supported by the loom's harness, and each has an eyelet through which the warp threads pass. The heddle is considered to be the most important single advance in the evolution of looms in general.