THERE WAS A BIG TURBULENCE IN HOLAKUS ATTACK TO IRAN, STARTING FROM KHORASAN AND NEYSHABUR; A LOT OF PEOPLE, SEARCHING FOR A SAFE SHELTER, WENT TO Ismaili FORTRESSESS WHAICH WERE RESISTANT AGAINST MONGOL TROOPS.KHAJI NASIR-AL-DIN TOUSI IS ONE OF THE BIGGEST SCHOLARS OF SHIIE IN 7TH CENTURY HIJRI, WHO IS SKILLED AND NOMINANT IN DIFFERENT SCIENCES. AS IT IS KNOWN HE WENT TO Ismaili TO SAVE HIMSELF AND USE THEIR RICH LIBRARIES, AND THEN HE HAS STUDIED AND WRITTEN DIFFERENT BOOKS. DURING THE TIME HE WAS LIVING IN GASTAN FORTRESS, REQUESTED BY NASIR-AL-DIN ABDOLRAHIM BIN MANSOUR, GAHISTAN GOVERNER, HE HAS TRANSLATED THE BOOK AL-TAHERE WRITTEN BY ABU ALI MASKUYE RAZI TO PERSIAN ANA SUMMARIED IT AND ADDED SOME PARTS TO IT LATER.THEN HE WENT TO ALAMOUT FORTRESS. THERE ARE DIFFERENT IDEA WHY KHALAJI WENT TO ALAMOUT FORTRESS. THIS STUDY DEALS WITH THE REASONS WHY KHAJI WENT TO Ismaili FORTESSES.