I. INTRODUCTIONBy the end of 1843, after half a century of successive wars and constant political turmoil and fiscal crisis, the Spanish infrastructure stock was meager and in very bad condition. It barely consisted of a network of paths that were unevenly distributed across the country. Of these paths only a small part was adapted to cart traffic, and an even smaller proportion actually deserved to be called roads. In addition, some small-scale ports and a few dams, canals and irrigation ditches completed the country's infrastructure endowment. Many of those structures were several centuries old by 1843, and some of them had their origin in former Roman works. As economists have long insisted, this sort of cost reduction, its dynamic long-term consequences and, specifically, the changes in the structure of location incentives that it produces, are absolutely crucial for growth. Thanks to the increase in infrastructure endowments, economies are allowed to exploit fixed resources that would otherwise remain idle due to the high transport costs. In addition, infrastructure allows a large share of non-agrarian production activities to concentrate in a few industrial centers, in a process that is absolutely crucial for the growth of developing economies and the rise of technologically advanced sectors. The next section offers a brief account of the methods that have been followed for the construction of the new series. Section III presents the main results of the estimation, and performs some sensitivity analyses. Finally, on the basis of the new figures, Section IV describes the main features of Spanish infrastructure investment and stock during the period under study. It is followed by a summary of the main conclusions, and an Appendix containing the complete series and the main sources that have been used to obtain them.