Napoleon’s lightning conquest of Prussia, accomplished within a month in the autumn of 1806, was perhaps his most spectacularly successful campaign. The twin battles of Jena and Auerstadt, won on the same day, October 14th, by Napoleon himself and his most able Marshal, Davout, annihilated the Prussian army and on 25th October, exactly a month after invading Prussia, Napoleon entered Berlin and enforced a humiliating peace on his beaten enemy. In his classic account of the campaign, published exactly 100 years ago, F. Loraine Petre explains how Prussia’s once vaunted military might ossified in the twenty years after Frederick the Great’s death, leading to timidity and political paralysis. What Field-Marshal Roberts in his foreword calls ‘a selfish and suicidal policy’ of ignoring France as she picked off neighbouring Austria led to defeat and occupation, but ultimately to much needed reform and the re-birth of the Prussian army with its ultimate revenge on Napoleon at Leipzig and Waterloo.