In the small hours of 17 September 1939, the Polish ambassador in Moscow was summoned and read a note. It said, in effect, that the Polish state had ceased to exist, and that therefore the agreements between the two countries no longer held. He declined to accept it. Within hours Soviet forces crossed the eastern frontier, sixteen days after Germany had crossed the western one.

That same night the Polish government left its own territory, crossing the bridge into Romania. Fighting in the east went on for about twenty days and ended in early October with the country divided between the two powers. Many thousands of Polish soldiers were killed; hundreds of thousands were taken prisoner, and in the months that followed large numbers of civilians were deported far from home. Some of those journeys never ended.

The map below is the kind of document that decides such things: a line drawn north to south, place names in another language, two signatures and a date in the corner. It is a small piece of paper for what it carried.