Metallic nanowires are of great interest as interconnects in nanoelectronic devices(1). They also represent important systems for understanding the complexity of electronic interactions and conductivity in one dimension(2). We have fabricated exceptionally long and uniform YSi(2) nanowires through self-assembly of yttrium atoms on Si(001). The wire widths are quantized in odd multiples of the Si substrate lattice constant. The thinnest wires represent one of the closest realizations of the isolated Peierls chain(3), exhibiting van Hove type singularities in the one-dimensional density of states and charge-order fluctuations below 150 K. The structure of the wire was determined through a detailed comparison of scanning tunnelling microscopy data and first-principles calculations. Quantized width variations along the thinnest wires produce built-in Schottky junctions, the electronic properties of which are governed by the finite size and temperature scaling of the charge-ordering correlation. This illustrates how a collective phenomenon such as charge ordering might be exploited in nanoelectronic devices.