A recent paper on the large-scale structure of the Universe presented evidence for a rectangular three-dimensional lattice of galaxy superclusters and voids, with lattice spacing 120 Mpc, and called for some "hitherto unknown process" to explain it. Here we report that a rectangular three-dimensional lattice of intersecting domain walls, with arbitrary spacing, emerges naturally as a classical solution of M-theory. 1999 Elsevier Science B.V. All rights reserved.