We report the formation of an ordered two-dimensional gold-silicon (Au/Si) alloy by deposition of a sub-monolayer of Si onto Au(111). Scanning tunneling microscope (STM) images show that at room temperature the Au/Si alloy consists of parallel rows with row-spacing 0.47 nm. These rows appear to float on Au(111) in bundles. Each bundle of rows can bend quite freely forming arches of arbitrary curvature. By annealing to 300 degrees C in ultra-high vacuum, the alloy changes its structure by forming straight rows with row spacing 0.35 nm. (C) 2011 Elsevier B.V. All rights reserved.