Nasir al-Din al-Tusi

Nasir al-Din al-Tusi (1201–1274), born Muhammad ibn Muhammad ibn al-Hasan al-Tusi in the city of Tus in northeastern Iran, was a Persian polymath whose work spanned architecture, philosophy, medicine, theology, and science. He authored extensively on mathematics, engineering, prose, and mysticism, and made notable advances in astronomy, including precise tables of planetary motion, an updated model of the heavens, and critiques of Ptolemaic astronomy. He also contributed to logic, mathematics—especially trigonometry—biology, and chemistry. Tusi is often credited with establishing trigonometry as a distinct mathematical field, and the scholar Ibn Khaldun ranked him as the greatest of the later Persian scholars. There is evidence suggesting his work may have influenced Copernican heliocentrism.

Tusi began his studies early in Tus and Hamadan, learning the Quran, Hadith, Ja'fari jurisprudence, logic, philosophy, mathematics, medicine, and astronomy. Born into a Shia family, he lost his father young and, honoring his father’s wish, pursued knowledge seriously, traveling to attend lectures of renowned scholars. He moved to Nishapur to study philosophy under Farid al-Din Damad and mathematics under Muhammad Hasib, met the Sufi master Attar of Nishapur, and attended lectures by Qutb al-Din al-Misri, a student of Al-Razi. In his work *Desideratum of the Faithful*, he wrote that becoming people of spiritual reality requires fulfilling the symbolic interpretation of the seven pillars of religious law, and that this is harder than simply obeying the law. In *Aghaz u anjam*, he explained that sacred accounts of history, perceived within space and time, symbolize events beyond such limits, expressed this way for human comprehension.

In Mosul, he studied mathematics and astronomy with Kamal al-Din ibn Yunus. He later corresponded with Sadr al-Din al-Qunawi, and, finding the Sufi mysticism of his time unappealing, composed his own manual of philosophical Sufism, *Awsaf al-Ashraf*. When Genghis Khan’s armies swept his homeland, Tusi was employed by the Nizari Ismaili state, moving between strongholds and making his most important scientific contributions—first in Quhistan, where he wrote the *Nasirean Ethics* in 1235, then at Alamut and Maymun-Diz under Nizari Imam Ala al-Din Muhammad. He was captured after Maymun-Diz fell to the Mongols under Hulegu Khan.

In his autobiography *The Voyage*, Tusi wrote that the destruction of the Alamut libraries in 1256 would not shake the Nizari Ismaili community, because they value the “living book” (the Imam of the Time) over the written word, attaching their hearts to the Commander of the Believers rather than the command itself. He asserted that a living Imam is always present in the world, and following him prevents a believer from going astray.

In 1256, when Alamut was attacked by Hulegu’s forces, some sources claim Tusi betrayed its defenses. After the castle fell, Hulegu, interested in natural sciences, appointed Tusi as his scientific adviser and a permanent member of his inner council. It is widely assumed Tusi accompanied the Mongols during the 1258 attack on Baghdad, playing an essential role in the end of the Abbasid empire. After the siege, he administered religious endowments, traveling to both Sunni and Shia institutions, and is credited with preserving religious foundations, libraries, and scholarly institutions under Mongol rule. Through his influence, he strengthened Twelver Shia intellectual life and institutional presence in Persia and Iraq without formally changing the state’s sectarian order.

Tusi produced about 150 works—25 in Persian, the rest in Arabic, and one treatise in Persian, Arabic, and Turkish. Among them are *Sayr wa-Suluk* (The Voyage), his autobiography; *Kitāb al-Shakl al-qattāʴ*, a five-volume summary of trigonometry; and *Al-Tadhkirah fi'ilm al-hay'ah*, a memoir on astronomy, which later received commentaries such as *Sharh al-Tadhkirah* by Abd al-Ali al-Birjandi and Nazzam Nishapur.