The way that rugs are made has remained relatively unchanged for thousands of years. Short pieces of colored wool are tied onto a pair of warp threads, by hand, using one of two simple knots. The work is done one row at a time. When a row is completed, the weft thread is inserted. It passes over the first warp, under the second, over and under to the end of the row. The length of the knot is then trimmed more or less to the desired pile height, the row is beaten down tight and the next row can begin.