Summary: We present a simple construction of long linear codes from shorter ones. Our approach is related to the product code construction; it generalizes and simplifies substantially the recent propagation rule by H. Niederreiter and C. Xing [Appl. Algebra Eng. Commun. Comput. 10, 425-432 (2000; Zbl 0965.94028)]. Many optimal codes can be produced by our method.