Can differences in beliefs about politics, particularly the benefits of war and peace, move markets? During the Siege of Paris by the Prussian army (1870–71) and its aftermath, we document that the price of the French 3% sovereign bond (rente) differed persistently between the Bourse in Paris and elsewhere, despite being one of the most widely held and actively traded financial assets in continental Europe. Further, these differences were large, reaching the equivalent of almost 1% of French GDP in overall value. We show these differences manifested themselves during the period of limited arbitrage induced by the Siege and persisted until the terms of peace were revealed.