O’Rourke gratefully acknowledges the financial support of the ERC, under the European Union’s Seventh Framework Programme (FP7/2007-2013), ERC grant agreement no. 249546; the Oxford History Faculty’s Sanderson Fund; and the John Fell OUP Research Fund. We also thank the staff of the Bodleian Library for their assistance, as well as Joseph Lane and Alexis Wegerich who very kindly helped us locate data. We are grateful to the following for their advice and support: Jim Anderson, Scott Baier, Richard Baldwin, Jamie Belich, Ana Carreras, John Darwin, Ron Davies, Simon Evenett, James Fenske, Kyoji Fukao, Oliver Grant, Paolo Guimaraes, Beata Javorcik, Morgan Kelly, Ju Kim, Jim Markusen, Thierry Mayer, Dennis Novy, Cormac Ó Gráda, Ferdinand Rauch, Tom Rutherford, Max Schulze, Kevin Tang, Alan Taylor, and Nikolaus Wolf; participants at the third CEPR Economic History Symposium, held in Oslo, the second OWL Economic History Workshop held at the University of Warwick, the workshop on “The Gravity Equation: Perspectives from Economic History and Trade” held at the University of St. Gallen, and the third Central Bank of Ireland Economic History Workshop; and seminar participants at the Graduate Institute in Geneva, Hohenheim, Humboldt, Mannheim, Oxford, Queens University Belfast, UC Irvine, and Vienna University of Economics and Business. The usual disclaimer applies. The views expressed herein are those of the authors and do not necessarily reflect the views of the National Bureau of Economic Research.