Austria invaded the Duchy of Warsaw with initial success. At the Battle of Raszyn on 19 April, Poniatowski's Polish troops brought an Austrian force twice their number to a standstill (but neither side defeated the other decisively), the Polish forces nonetheless retreated, allowing the Austrians to occupy the Duchy's capital, Warsaw, as Poniatowski decided that the city would be hard to defend, and instead decided to keep his army mobile in the field and engage the Austrians elsewhere, crossing to the eastern (right) bank of the Vistula. In a series of battles (at Radzymin, Grochów and Ostrówek), the Polish forces defeated elements of the Austrian army, forcing the Austrians to retreat to the western side of the river.