 The Mongol army pressed on after the monsoon season . In the following dry season of 1277 – 78 , c . December 1277 , a Mongol army of 3800 led by Nasr al @-@ Din , son of Gov. Sayyid <unk> , advanced to <unk> , which defended the <unk> Pass . They occupied the fort and destroyed a large number of abandoned stockades . But they found the heat excessive and returned . 
