 Mackensen believed that the Serbian forces still could be surrounded and destroyed, he had hoped that the Serbs would make a stand at Kragujevac, but on 31 October, it became clear that Putnik had decided to withdraw further.While determined rearguards held off the forces pressing down on him from the north, the Serbian Chief of the General Staff ordered the rest of the army to pull back towards Kosovo.Mackensen’s chose to order a vigorous pursuit in the Ibar Valley, with the aim of encircling and fighting a decisive final battle against the Serbs in the Kosovo area near Priština, known as the “Field of Blackbirds”.