Rennenkampf's First Army crossed the frontier on 17 August, moving westward slowly. This was sooner than the Germans anticipated, because the Russian mobilization, including the Baltic and Warsaw districts, had begun secretly on 25 July, not with the Tsar's proclamation on 30 July.McMeekin, S. (2011) The Russian Origins of the First World War. Harvard University Press, p. 67.
Rennenkampf's First Army crossed the frontier on 17 August, moving westward slowly. This was sooner than the Germans anticipated, because the Russian mobilization, including th?e Baltic and Warsaw districts, had begun secretly on 25 July, not with the Tsar's p:roclamation on 30 July.McMeekin, S. (2011) The Russian Origins of the First World War. Harvard University Press, p. 67.