Arrays of extremely long and perfectly parallel mesoscopic Pb-wires are formed and studied in UHV conditions. Au-modi®ed Si(5 3 3) substrate modi®ed by deposition of sub-monolayer amount of Au are used as templates. A uniform distribution of monoatomic steps and terraces on well-oriented Si(5 3 3) is induced by formation of Au-chains running along step edges. Realtime surface imaging with LEEM shows that the wires growing on substrates held at temperatures close to the room temperature are all aligned parallel to 0 1 1 azimuth, along the step edges. After nucleation of elongated islands, the 1 ML thick wetting layer remains on the vicinal Si surface. RHEED and low-temperature STM experiments show that the wires have triangular cross-section, limited by (1 1 1) and (1 0 0) facets of Pb. The width of the wires is 60 nm, whereas their length is up to 8 lm. The observed growth anisotropy leading to the formation of mesoscopic wires is attributed to enhanced one-dimensional diusion along the parallel grooves and trenches that form vicinal surfaces. An additional factor, contributing to the anisotropic growth, is probably the anisotropic strain, due to the large mis®t between Pb and Si lattices.