 The Germans had begun massing troops near the Soviet border even before the campaign in the Balkans had finished. By the third week of February 1941, 680,000 German soldiers were gathered in assembly areas on the Romanian-Soviet border. In preparation for the attack, Hitler moved more than 3.2 million German and about 500,000 Axis soldiers to the Soviet border, launched many aerial surveillance missions over Soviet territory, and stockpiled war materiel in the East.
