With Alamut now in his possession, Hassan swiftly embarked on a complete re-fortification of the complex.
By enhancing the walls and structure of a series of storage facilities, the fortress was to act as a self-sustaining stronghold during major confrontations.
The perimeters of the rooms were lined with limestone, so as to preserve provisions to be used in times of crisis.
Indeed, when the Mongols invaded the fortress, Juwayni was astonished to see stored countless supplies in perfect condition to withstand a possible siege.
Recent work by Iranian archeologists at the northern gate of the fortress revealed two interconnected cellars, likely used as private spaces or for food storage.

Next, Hassan took on the task of irrigating the surrounding villages of the Alamut valley.
 The land at valley's floor was arable land, allowing for the cultivation of dry crops including barley, wheat and rice.
In order to make available the maximum amount of cultivable land, the ground was terraced under Hassan's direction.
The sloping valley was broken up into step-like platforms upon which abundant food could be cultivated.
In times of need the surrounding villages were well equipped to furnish the castle with ample supplies.

The construction of Alamut's famous library likely occurred after Hasan's fortification of the castle and its surrounding valley.
With its astronomical instruments and rare collection of works, the library attracted scholars and scientists of a variety of religious persuasions from around the world who visited it for many months at a time, hosted by the Isma'ilis.
By and large the writings of the Persian Ismailis, both scientific and doctrinal, did not survive beyond the Alamut period.
In addition to the rich literature they had already produced in Arabic, the relocation of the Ismaili center to Iran now prompted a surge in Persian Ismaili literature.
The bulk of Nizari writing produced in this period, however, was lost or destroyed during the Mongol invasions.
While the majority of Alamut's theological works on Ismailism were lost during the library's destruction, a few significant writings were preserved including the major anonymous work of 1199 AD entitled Haft Bāb-i Bābā Sayyidnā and a number of treatises by Nasir al-Din al-Tusi.

One of the earliest losses of the library came during the early years of the Imam Jalal al-Din Hasan’s leadership at Alamut.
In keeping with his principles of bridging the gaping relations between the Persian Ismailis and the broader Sunni world, Imam Jalal al-Din Hasan invited a number of religious scholars from the town of Qazvin to visit the castle's library and burn any books they deemed heretical.
However, it was not until under the direction of the Mongol ruler, Hulegu Khan, when the Mongols ascended to the fortress in December 1256 AD, that the Alamut library was lost.
With the permission of Hulegu, Juvayni explored the library and selected a few works he deemed worthy of salvaging, before the remainder was set aflame.
His choice items included copies of the Qur'an, a number of astronomical instruments and treatises, and a number of Ismaili works.
 An anti-Ismaili, Ata-Malik Juvayni's personal leanings were the sole measure of heretical content of the library's doctrinal works.
Thus, some of the richest treatises regarding the tenets of Ismaili faith were lost with his destruction of the library.
From his tour and survey of the castle, Juvayni compiled a description of Alamut that he incorporated into his chronicle of the Mongol invasions, entitled Tarikh-i Jahangushay-i Juvaini ("The History of the World Conqueror").
With Alamut now in his possession, Hassan swiftly embarked on a complete re-fortification of the complex. By enhancing the walls and structure of a series of storage facilities, the fortress was to act as a self-sustaining stronghold during major confrontations. The perimeters of the rooms were lined with limestone, so as to preserve provisions to be used in times of crisis. Indeed, when the Mongols invaded the fortress, Juwayni was astonished to see stored countless supplies in perfect condition to withstand a possible siege. Recent work by Iranian archeologists at the northern gate of the fortress revealed two interconnected cellars, likely used as private spaces or for food storage.
Next, Hassan took on the task of irrigating the surrounding villages of the Alamut valley.  The land at valley's floor was arable land, allowing for the cultivation of dry crops including barley, wheat and rice. In order to make available the maximum amount of cultivable land, the ground was terraced under Hassan's direction. The sloping valley was broken up into step-like platforms upon which abundant food could be cultivated. In times of need the surrounding villages were well equipped to furnish the castle with ample supplies.
The construction of Alamut's famous library likely occurred after Hasan's fortification of the castle and its surrounding valley. With its astronomical instruments and rare collection of works, the library attracted scholars and scientists of a variety of religious persuasions from around the world who visited it for many months at a time, hosted by the Isma'ilis. By and large the writings of the Persian Ismailis, both scientific and doctrinal, did not survive beyond the Alamut period. In addition to the rich literature they had already produced in Arabic, the relocation of the Ismaili center to Iran now prompted a surge in Persian Ismaili literature. The bulk of Nizari writing produced in this period, however, was lost or destroyed during the Mongol invasions. While the majority of Alamut's theological works on Ismailism were lost during the library's destruction, a few significant writings were preserved including the major anonymous work of 1199 AD entitled Haft Bāb-i Bābā Sayyidnā and a number of treatises by Nasir al-Din al-Tusi.
One of the earliest losses of the library came during the early years of the Imam Jalal al-Din Hasan’s leadership at Alamut. In keeping with his principles of bridging the gaping relations between the Persian Ismailis and the broader Sunni world, Imam Jalal al-Din Hasan invited a number of religious scholars from the town of Qazvin to visit the castle's library and burn any books they deemed heretical. However, it was not until under the direction of the Mongol ruler, Hulegu Khan, when the Mongols ascended to the fortress in December 1256 AD, that the Alamut library was lost. With the permission of Hulegu, Juvayni explored the library and selected a few works he deemed worthy of salvaging, before the remainder was set aflame. His choice items included copies of the Qur'an, a number of astronomical instruments and treatises, and a number of Ismaili works.  An anti-Ismaili, Ata-Malik Juvayni's personal leanings were the sole measure of heretical content of the library's doctrinal works. Thus, some of the richest treatises regarding the tenets of Ismaili faith were lost with his destruction of the library. From his tour and survey of the castle, Juvayni compiled a description of Alamut that he incorporated into his chronicle of the Mongol invasions, entitled Tarikh-i Jahangushay-i Juvaini ("The History of the World Conqueror").
Alamut Castle