 The 5th Mountain Division , together with the reinforced 125th Infantry Regiment , crossed the Struma river under great hardship , attacking along both banks and clearing bunkers until they reached their objective on 7 April . Heavy casualties caused them to temporarily withdraw . The 72nd Infantry Division advanced from <unk> across the mountains . Its advance was delayed by a shortage of pack animals , medium artillery and mountain equipment . Only on the evening of 9 April did it reach the area north @-@ east of Serres . Most fortresses — like Fort <unk> , <unk> , <unk> , <unk> , <unk> , <unk> , <unk> and <unk> — held until the Germans occupied Thessaloniki on 9 April , at which point they surrendered under General Bakopoulos ' orders . Nevertheless , minor isolated fortresses continued to fight for a few days more and were not taken until heavy artillery was used against them . This gave time for some retreating troops to evacuate by sea . Although eventually broken , the defenders of the Metaxas Line succeeded in delaying the German <unk> Metaxas Line , requiring 150 @,@ 000 men , could have held out longer , but the bulk of the Greek army was facing the Italians in Albania . 
