The Romanian Bridgehead was an area in southeastern Poland, now located in Ukraine. September 14, 1939 the Polish Commander in Chief Marshal of Poland Edward Rydz-Śmigły ordered all Polish troops fighting east of the Vistula (approximately 20 divisions still retaining cohesion) to withdraw towards Lwów (now in Ukraine), and then to the hills along the borders with Romania and the Soviet Union.
The plan was that the Polish forces would be able to organise a successful defence until the winter, and hold out until the promised French offensive on the Western Front started. However, the Soviet invasion of Poland on September 17 made those plans obsolete. As a result, Polish units were ordered to evacuate Poland and reorganize in France.
Up to 120,000 Polish troops withdrew to neutral Romania and Hungary. The majority of those troops joined the newly-formed Polish Armed Forces in the West. Until the United States, the Polish army was one of the largest forces of the Allies.
more at Wikipedia
