On this day (11 September) in the year 9 A.D. the Romans suffer their greatest defeat at the Battle of the Teutoburg Forest; thereafter the Rhine is established as the de facto border between the Roman Empire and the so-called barbarians for the next four hundred years.

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On this day (8 October) in 1939, Nazi Germany annexed western Poland and the Free City of Danzig–92,500 square kilometers in all. Most of the remainder of Poland (over 200,000 square kilometers) was annexed by the Soviet Union. More details, via Wikipedia, are available here: https://en.wikipedia.org/wiki/Polish_areas_annexed_by_Nazi_Germany