سِيرَةُ نَصِيرِ الدِّينِ الطُّوسِيّ — أَبُو جَعفَرٍ مُحَمَّدُ بنُ مُحَمَّدٍ الطُّوسِيُّ النَّصِيرُ [597-672هـ / 1201-1274م]: الفَيلَسُوفُ الإِسمَاعِيلِيُّ وَمُؤَسِّسُ مَرصَدِ مَرَاغَة
Seerah Nasir al-Din al-Tusi (سِيرَةُ نَصِيرِ الدِّينِ الطُّوسِيّ; full name: Abu Ja'far Muhammad ibn Muhammad ibn al-Hasan al-Tusi, with the honorific Nasir al-Din [Supporter of the Faith]; born 597 AH / 1201 CE in Tus [Khurasan, present-day Iran]; died 672 AH / 1274 CE in Baghdad; among the most wide-ranging scholars of the medieval Islamic world: philosopher, theologian, mathematician, astronomer, and scientist; his Ismaili period at Alamut: around 1226 CE [when he was approximately 25 years old], al-Tusi came to live at the Ismaili strongholds in the mountains of northern Persia [at Alamut and related fortresses under the Nizari Ismaili Imams]; the circumstances are debated: some classical sources [hostile to the Ismailis] claim he was taken prisoner; other accounts suggest he came voluntarily as a scholar seeking patronage and intellectual freedom; during his time at Alamut [c. 1226-1256 CE — approximately 30 years], al-Tusi was under the patronage of the Nizari Ismaili Imams [Imam Nizar al-Din 'Abd al-Salam, Imam 'Ala' al-Din Muhammad, and Imam Rukn al-Din Khurshah]; he produced his most important philosophical and theological works during this period; Rawdat al-Taslim [Paradise of Submission]: written during the Alamut period; title: Rawdat al-Taslim [رَوضَةُ التَّسلِيم — Paradise of Submission]; also known as Tasawwurat [Conceptions/Representations]; content: the most sophisticated philosophical exposition of Nizari Ismaili doctrine produced in the classical period; topics: the nature of ta'wil and tanzil; the cosmological hudud; the Imam's function in the cosmos; the path of walayah; eschatology from an Ismaili perspective; significance: the work represents the intellectual maturation of Ismaili philosophy at the point when Greek philosophy [Aristotle, Neoplatonism] had been fully integrated with Ismaili doctrine; al-Tusi brings Avicennan philosophy and Ismaili theology into a unified framework; it was written in Persian [not Arabic] — one of the first major Ismaili theological texts in Persian; Mongol invasion and the fall of Alamut: in 1256 CE, Hulagu Khan's Mongol forces arrived at Alamut; the last Nizari Imam at Alamut [Imam Rukn al-Din Khurshah] surrendered; Alamut was destroyed; al-Tusi survived and entered Mongol service; his motivation and the ethical complexities: al-Tusi's entry into Mongol service after the fall of Alamut is one of the most contested decisions in his biography; some accounts suggest he facilitated the surrender; others that he merely survived and made the best of it; al-Tusi is reported to have said 'I serve whoever destroys what I dislike' — which may have meant the Ismaili political establishment that confined him, or may be hostile tradition; what is clear: al-Tusi served Hulagu Khan and was instrumental in establishing the Maragha Observatory; the Maragha Observatory: founded c. 1259 CE under Hulagu Khan's patronage at Maragha [northwestern Iran]; director: Nasir al-Din al-Tusi; the world's first large-scale astronomical research institution; features: a large library [reportedly 400,000 volumes]; sophisticated instruments; an international team of scholars [Chinese, Persian, Greek-heritage]; produced: [1] Zij-i Ilkhani [زِيجِ اِيلخَانِيّ — The Ilkhanid Astronomical Tables]: comprehensive astronomical tables for calculating planetary positions; used for over a century across the Islamic world; [2] al-Tadkira fi 'Ilm al-Hay'a [التَّذكِرَةُ فِي عِلمِ الهَيئَة — Memoir on Astronomy]: al-Tusi's major astronomical treatise; introduces the 'Tusi couple'; the Tusi couple: a mathematical device developed by al-Tusi to explain linear motion as a combination of two circular motions; the problem: Ptolemy's astronomical model required 'equant points' — points around which planetary motion was uniform but that were not the center of the circular orbit; this violated the principle that all celestial motion should be uniform circular motion; al-Tusi's couple solved this problem geometrically; significance: Nicolaus Copernicus [1473-1543 CE] used a geometrically identical device in his heliocentric model [De Revolutionibus, 1543]; this is almost certainly not coincidental — al-Tusi's astronomical work reached Renaissance Europe through Arabic-Latin translations; philosophy: al-Tusi's Tajrid al-I'tiqad [تَجرِيدُ الاِعتِقَادِ — Abstraction of Beliefs] became the standard text of Shi'i kalam; commentaries on it were written for centuries; Akhlaq-i Nasiri [الأَخلَاقُ النَّاصِرِيَّة — Nasirean Ethics]: al-Tusi's comprehensive ethical treatise; draws on Aristotle's Nicomachean Ethics; in the tradition of Islamic virtue ethics; among the most read ethical works in classical Persian-Islamic culture) is the medieval world's most improbable survivor and its most consequential institutional founder.
The Philosopher of Alamut
Nasir al-Din al-Tusi spent approximately 30 years at the Ismaili mountain fortresses of Alamut and allied strongholds, under the patronage of the last Nizari Ismaili Imams. During this period, he produced Rawdat al-Taslim (Paradise of Submission) — the most philosophically sophisticated exposition of Nizari Ismaili doctrine from the classical period. Written in Persian rather than Arabic, it represents the full integration of Avicennan philosophy and Neoplatonism with Ismaili theology: the nature of ta’wil and tanzil, the cosmological hudud, the Imam’s function in the cosmic order, the path of walayah, and an Ismaili eschatology.
Whether al-Tusi came to Alamut voluntarily or under some form of compulsion remains contested. What is clear is that intellectually, he thrived there. Rawdat al-Taslim is not the work of a reluctant prisoner but of a scholar who had found a framework that genuinely engaged him.
The Tusi Couple and Copernicus
In 1259 CE, three years after the Mongol destruction of Alamut, al-Tusi founded the Maragha Observatory under Hulagu Khan’s patronage. This was the world’s first large-scale astronomical research institution — a library of reportedly 400,000 volumes, sophisticated instruments, and an international team of scholars.
At Maragha, al-Tusi developed the device now known as the “Tusi couple” — a geometric construction showing how linear motion can be produced by two circular motions. He devised this to solve a deep problem in Ptolemy’s astronomical model: the “equant” violated the principle that all celestial motion must be uniformly circular. The Tusi couple solved it geometrically. Centuries later, Copernicus used an geometrically identical device in his heliocentric model (De Revolutionibus, 1543). Historians of science now believe this is not coincidental — al-Tusi’s astronomical work reached Renaissance Europe through Arabic manuscripts.
The Ethics of Survival
Al-Tusi’s entry into Mongol service after Alamut’s fall is one of Islamic intellectual history’s most ethically complex episodes. He survived a catastrophe that destroyed the political structure he had lived within for 30 years, and then became instrumental in building one of Islamic civilization’s greatest scientific institutions under the conqueror’s patronage. The judgment of this choice by later scholars has been varied.
See also: Tawil Esoteric Interpretation, Bayah And Walayah, Ismaili Cosmology Hudud Al Din, Seerah Al Kindi, Seerah Ibn Sina