The citadel of Almut standing amidst the lofty Caucasus was the stronghold of the Ismailis, where Hasan ibn Sabha and his followers (Assassins) had built their earthly paradise. This inaccessible stronghold which for centuries had successfully defied the successive invasions was at last captured by Hulaku Khan, the Mongol in 1256 A.C. A long line of prisoners tied with one another was paraded before the Mongol tyrant, Among them was a middle-aged man peculiarly dressed, who being ushered in Hulaku’s presence impressed him with his great eloquence and extraordinary intelligence. The man introduced to him was Nasir al-Din Toosi, a versatile genius and above all, a capable astrologer, who could foretell the fortune of the Mongol conqueror. Hulaku, finding Nasir al-Din to be a very useful person took him in his retinue and kept him as his trusted Adviser throughout his life.

Nasir al-Din Toosi, one of the great thinkers of Islam, was a man of towering ability whose encyclopedic work embraced almost all branches of knowledge, including astronomy, mathematics, sciences, optics, geography, medicine, philosophy, logic, music, mineralogy, theology and ethics.

Abu Jafar Muhammad ibn Muhammad al Hasan Nisar al-Din al-Toosi al-Muhaqqiq (the Investigator) was born on February 18, 1201 A.C. in Toos, a city of Khorasan where he received his early education. His principal teacher was Kamal al-Din ibn Yunus. His fame as a versatile scholar and astrologer soon spread to the distant parts of Persia and he was kidnapped by Nasir al-Din Abd al-Rahman ibn Ali Mansur, the Ismaili Governor of Kohistan, who despatched him to Almut, where he remained as an unwilling guest for a long time. In 1256 A.C. when Almut was captured by Hulaku Khan, he entered the service of the Mongol conqueror and remained his trusted Adviser. In February 1258, when Baghdad capitulated to the Mongols and was sacked by them, Nasir al-Din Toosi who accompanied them was greatly instrumental in influencing Hulaku, to spare a part of its population as well as the Shiite sanctuaries in Southern Iraq.

Hulaku appointed Toosi as his Wazir and Supervisor of Wakf Estates. It was under his orders that Toosi at the age of sixty set about building in 1259– one year after the sack of Baghdad, on the fortified Maragha Hill, the world-famous observatory popularly known as the Maragha observatory. It was equipped with the best available instruments and staffed by some of the prominent astronomers of the age who carried on most important astronomical researches under the direction and supervision of Toosi.

Toosi retained his influence in the Mongol Court even under Abaka without interruption until his death on June 26, 1274 A.C. in Baghdad.

Nasir al-Din Toosi was an outstanding encyclopaedist with a fine synthetic brain. He was a prolific writer; not less than 56 of his works are listed by Brockalmann. A large number of his treatises are not included in this list. He had made a thorough study of Greek learning and had translated as well as edited a number of Greek works, into Persian. This collection of translations is called ‘Kitab al Mutawassitat Bain al Handasa wal Hai-a’ (The middle books between geometry and astronomy). He discussed scientific matters with the celebrated Sufi poet Jalaluddin Rumi through correspondence, and with Najam al-Din Katibi orally. He dedicated his ‘Talkhis Muhassal’ to the historian Alauddin and his ‘Awsaf al-Ashraf’ to Sahib Diwan Shamsuddin. His fame as one of the greatest intellects of Islam rests on his researches in astronomy, astrology, mathematics, physics, medicine and exact sciences.

It is in astronomy that Nasir al-Din Toosi acquired great fame and made lasting contributions. His practical work and invaluable researches in the subject owed much to the interest of Mongol Rulers, especially Hulaku. He took 12 years to complete his new ‘Planetary Tables’ known as ‘Nkhanian Tables’.

He wrote a number of astronomical treatises of which the most important is ‘Kitab al Tazkira al Nasirya’ or ‘Tazkira film a haira’ (Memorial of Astronomy) a survey of the whole field of astronomy on which numerous scholars have written commentaries and which has been translated into several Eastern as well as Western languages. The book was named after his first patron Nasir al-Din, Governor of Kohistan. Hence the book which had two editions was written before 1256 A.C. ‘Tazkira,’ which forms a landmark in the development of astronomy, won great popularity throughout the East and the West. A large number of its commentaries were written by renowned scholars, including ‘Bayan Maqasid Tazkira’ (Explanation of the Aims of Tazkira, by Muhammad ibn Ali Husain al Himadhi, with notes by Mahmood ibn Masud Qutbuddin al-Shirazi (d. 1310-11); the ‘Tanzih al Tazkira’ (Illustration of the Tazkira) written in 1311-12 by al Hasan ibn Muhammad Ali Nishapuri. A commentary in Turkish language was written by Fath Allah Sherwani in 1414 A.C. A large number of commentaries assisted in the assimilation of “Tazkira” which is very condensed. This book is divided into four large chapters dealing with

  1. ‘Geometrical and cinematical introduction with discussions of rest, simple and complex motions’
  2. ‘General astronomical notions-secular change of the obliquity of the ecliptic, trepidation of the equinoxes’. A part of this chapter which was translated by Carr De Vaux, bristles with scathing criticism of Almagest written by Ptolemy. The learned Toosi corrected the views regarding the anomalies of the Moon and the motion in latitude of the planets as contained in Almagest’
  3. ‘Earth and the influence of celestial bodies on it. It also contains accounts of seas, winds, tides and how these are caused’
  4. ‘The size and distances of the planets’

His forceful criticism of Ptolemic astronomy paved the way for the Copernican reform. He has written a large number of astronomical treatises including

  1. ‘Zubdat al Hai’a (The Cream of Astronomy)
  2. ‘Kitab al Tahsil fil Najum’ (The Stars made Easy)
  3. ‘On the Trajectory, Size and Distance of Mercury’
  4. ‘Parts of Mutawassit’
  5. ‘Rising and Setting’
  6. ‘On the Moving Sphere’
  7. ‘On the Size and Distances of Sun and Moon’; ‘Phenomena’
  8. ‘On the Ascension of Stars’
  9. ‘Spherics’
  10. ‘Days and Nights’
  11. ‘Habitations’
  12. ‘Tahzir al Majisti’
    This book contains criticism of Ptolemy’s views. His ‘Zubdat al Hai-a’ is extant in Arabic and Persian.

The fame of Nasir al-Din Toosi in astronomy rests chiefly on his astronomical researches carried on in the Maragha observatory. The destruction wrought by the Mongol hordes served as a death blow to all cultural and intellectual movements in the world of Islam. Their cultural treasures amassed during centuries of intellectual pursuits were reduced to ashes on the fall of Baghdad. Together with Darul Hukame of Baghdad, founded by Mamoon ar-Rashid in the first half of the 9th century and ‘Bait-ul-Hukama’ of Cairo, established by the Fatimid Caliph Al-Hakam in the first half of the 11th century, the observatory of Maragha was the third greatest center of literary and astronomical research in the East. This Khaniz observatory was completed in 1259 A.C. Its remains are still extant. This observatory was equipped with the best available instruments, including an “armillary sphere, the mural quadrant, and a solstitial armil,” which were probably brought from Baghdad and Almut. It also housed a big library, which, according to Ibn Shakir, contained more than 400,000 books, collected by the Mongol armies from Syria, Iraq, and Persia. The Khaniz observatory of Maragha functioned under Toosi who was its first Director and was later on succeeded by his two sons. It was staffed by some of the eminent astronomers of the age, including Mohi al-Din al-Maghribi and the illustrious Abul Faraj. The instruments used in this observatory have been described by al Urdi and Khwandmir which included ‘Tamathil-i-Ashkal-i-aflak’; ‘Hawamil’ (deferents); ‘Dawairi Mauhuma wa Suwar wa Buruj-i-duwaz’ (Imaginary Circles, Constellations, and Signs of the Zodiac).

He is reputed as the inventor of the Turquet (Torquetum), an instrument containing two graduated circles in two perpendicular planes, which became very popular in the West during the 15th and 16th centuries, towards perfecting their instruments. “They endeavored to make their instruments as large as possible,” writes Carra De Vaux, “In order to minimize error; they then began to make special instruments, each being devoted to special class of observations. In the observatory at Maragha, there were instruments made of rings for special purposes; ecliptical, solstitial, and equatorial armillaries. The ecliptical, which were very much used, had five rings, the largest of which was some 12 feet across. It was graduated in degrees and minutes. When Alfonso of Castilla wanted to construct an armillary sphere, which would be finest and best that had yet been made, it was to the Arabs that he turned for information”

The principal research carried on in the Maragha observatory which lasted for two generations only, related to the compilation of ‘Al Zij-al-Ikhani’ better known as ‘The Ikhanian Tables’, which earned great popularity throughout the East, including China. This Table was compiled by Nasir al-Din Toosi after 12 years of hard research and was completed in 1272 A.C. The original text was probably written in Persian. This work is divided into four books namely,

  1. Chinese, Greek, Arabic and Persian Chronology,
  2. Motions of the Planets,
  3. Ephernerides,
  4. Astronomical Observations.
    This Table was translated into Arabic and several commentaries were written on it.

His other important astronomical works regarding calendar are

  1. ‘Mukhtasar fi Im al Tanjim wa Marifat al-Taqwim’ (Summary of Astrology and of the Calendar) which is extant in Persian; and
  2. ‘Katab al-Barifi Ulum al-Taqwim wa Harakat al Aflak wa-Ahkam al Nujum’(The excellent book on the Calendar, the Movement of the Spheres and Judicial Astrology). This Astrological treatise ‘Kitab-i-si-Fasl,’ is a work of high order.

Only next to astronomy stands Nasir al-Din’s contribution to mathematics. He has left behind him immortal works on geometry and trigonometry. He edited most of the ancient mathematical works numbering 16, which included four books of the Muslim period. He wrote four treatises, on arithmetic and algebra, including ‘Al Mukhtasar bi Jami al Hisab bil Takht wal Turab’, (Summary of the whole of Computation with Table and Earth) and ‘Kitab al Jabr wal Muqabala’ (Treatise on Algebra). The first one is extant in Arabic and Persian.

He is equally important as a geometer. He wrote no less than fifteen treatises on geometry, which included his ‘Al Usul ul Maudua’ (Treatise on Euclids Postulates); ‘Qawaid-al-Handasa’ (Principles of Geometry) and ‘Tahrir al Usual’ (the two Reductions of the Elements of Euclid) in which, contrary to the principle followed by Euclid, he multiplied the special cases.

Nasir al-Din Toosi played no small part in the advancement of trigonometry. His works on trigonometry marked the culmination of the progress in the subject. He is the author of the ‘Kitab Shakl al Qatta’ (A treatise on Quadrilateral) an extremely original work in which trigonometry has been treated independently of astronomy. The book dealing with spherical trigonometry is very .comprehensive and perhaps the best work on the subject written during the medieval times. It was translated into French and edited by Alexandre Cara Theodory Pasha in 1891. Writing in the Legacy of Islam, Carra De Vaux says, “Trigonometry, plane or spherical, is now well established and finds in this book its first methodically developed and deliberate expression”. This treatise of Nasir al-Din had a deep influence over the mathematicians of both the East and West who based their trigonometrical researches on this book.

“To appreciate Nasir al-Din’s achievements”, admits George Sarton, it will suffice to realize that his ‘Shakl al-Qatta’ was almost the Arabic equivalent of ‘Regiomontanus’, ‘De Triangulis Omnimodis Libri Quinque, posthumously printed in 1533.

Being a versatile genius, Nasir al-Din Toosi has made lasting contributions to optics, occult sciences, mineralogy, medicine, geography, music, philosophy, theology and ethics. In optics, he has left behind three treatises namely ‘Tahrir Kitab al Manazir’ Mabahith Fin ‘ikas al Shu’aat wa in Itafiha’ (Research on the Reflection and Deflection of Rays) and reply to Ali ibn Umar al Qazwini. All these treatises have been translated into the German language by Eilhard Wiedemann.

He wrote probably two treatises on music, namely ‘Kitab fi Ilm al Mausiqi’ which was written in Arabic and ‘Kanz al Tuhaf’, written in Persian. His musical theories were elaborated and enlarged by his celebrated disciple Qutab al-Din al-Shirazi. He is said to have invented a flute known as ‘Mahtar Duduk’(Chapel Flute).

A chapter of his Tazkira deals with geodesy describing the seas, winds the tides. His medical works are of no less scientific importance. He wrote ‘Kitab al-Bab Bahiya fil Tarakib al Sultaniya’, a regimen divided into three parts which deal with diets, health rules, and sexual intercourse. This book was translated into Turkish language.

His two treatises deal with logic. These are ‘Kitab al Tajrid fi Ilm al Mantiq’(Compendium of Logic) and commentary on the ‘Katab Alisharat wal Tanbihat’, written by Ibn Sina. His ‘Akhlaq-i-Nasiri’ classifies knowledge into speculation and practical. The speculative knowledge he has subdivided into

  • Metaphysics and Theology
  • Mathematics (including music, optics and mechanics)
  • Natural Sciences which included Elements, Science of Transformations, Meteorology, mineralogy, botany, zoology, psychology, medicine, astrology and agriculture.
    The practical knowledge included (a) ethics, (b) domestic economy, and (c) politics.

In order of importance, his large number of philosophical, metaphysical, and theological treatises rank only next to his works on astronomy and mathematics. In orthodox circles of his sect, his fame chiefly rests on these treatises. His ‘Kitab al Fusul’ dealing with metaphysics was written in Persian which was translated into Arabic by Al-Jurjani. His monumental philosophical work ‘Tajrid al Aqaid’ (Al Kalam) is his most popular work on which a large number of commentaries have been written in Arabic, Persian and Turkish languages. The best commentary was written by Ali ibn Muhammad Al-Jurjani. His outstanding work on ethics entitled ‘Akhlaq-i-Nasiri’ (Nasirian Ethics) is one of the best books written on the subject which still serves as a text-book in Arabic schools throughout the Islamic world. This was written before 1256 and translated into Arabic as Risala fil Tahqiq-al Ilm. Together with Akhlaq-i-Jalali, this invaluable ethical treatise of Nasir al-Din Toosi is one of the two most popular works on the subject in the East. Several editions of this book were printed in India and parts of it were also translated and published in the English and German languages.

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