The position of the Greek First Army, still fighting in Albania, was seriously jeopardized by the rapid advance of the XL Panzer Corps via Florina and by the British withdrawal to positions behind the Aliakmon. The Greek command therefore had to come to grips with the necessity of withdrawing southward from Albania. However, it was not until 13 April that the first Greek elements began to withdraw toward the Pindus Mountains. On the next day an advance detachment of the 73d Infantry Division encountered Greek troops withdrawing from Albania across the Pindus Mountains into the area west of Kastoria. Heavy fighting took place on that and the following day, especially at Kastoria Pass, where the Germans blocked the Greek withdrawal, which by then extended to the entire Albanian front, with the Italians in hesitant pursuit.