In late March 1241, Mongol forces, which had previously been divided into two armies, reunited in the area of Krakow. On April 1, the invaders headed westwards, to the Polish province of Silesia. After a skirmish near Raciborz, the Mongols decided not to besiege well-fortified Raciborz. Instead, they followed the Oder towards Opole. There, they faced units from Lesser Poland (the provinces of Krakow and Sandomierz), reinforced with knights of Duke of Opole, Wladyslaw. Since the Poles were numerically inferior, they retreated after a short battle. The Mogols followed them towards Wroclaw, and Legnica (see Battle of Legnica).