The Mongol Service viewpoint holds that Nasir al-Din al-Tusi (1201-1274), the Persian polymath, astronomer, and philosopher, made a rational, defensible, and ultimately beneficial choice when he entered the service of the Mongol il-khans - most consequentially by accompanying Hulagu Khan's forces during the siege and sack of Baghdad in 1258. Holders of this view argue that Tusi's collaboration with the Mongols was not treachery or moral failure but a calculated act of intellectual self-preservation and cultural stewardship that saved an irreplaceable body of Islamic learning. This position is held by a number of historians of Islamic science and medieval philosophy, as well as scholars sympathetic to the pragmatic ethics of survival under conquest.

Proponents argue that Tusi had little meaningful agency in his initial entry into Mongol-adjacent service. He had spent years effectively imprisoned by the Ismaili Nizari ruler Muhtasham at Alamut, where he was compelled to produce works under a kind of learned captivity. When Hulagu's forces took Alamut in 1256, Tusi's transfer into Mongol service represented, on this reading, liberation rather than collaboration. He did not seek out a conquering power; he was delivered into one set of masters by the destruction of another.

The central affirmative argument is that Tusi's service to Hulagu produced the Maragha Observatory, founded around 1259, which became the most sophisticated astronomical institution in the medieval world. Tusi used Mongol patronage to assemble a library of some 400,000 volumes - many rescued from Baghdad and other conquered cities - and to gather scholars from across the Islamic world and beyond, including Chinese astronomers. Holders of this view contend that without Tusi's proximity to Hulagu, this institutional and intellectual infrastructure would not have existed, and the transmission of Islamic science into the early modern period would have been substantially impoverished. The planetary models developed at Maragha, including Tusi's own geometric device (the “Tusi couple”), are held to have influenced Copernicus directly or indirectly, making the observatory's output of consequence to the entire history of science.

This viewpoint draws on a broader ethical framework in which collaboration with illegitimate or violent power is judged not by the character of the patron but by the use to which the collaboration is put. Tusi, on this account, extracted from Mongol conquest the maximum possible benefit for learning and civilization while bearing no personal responsibility for the violence that created the conditions of his service. Advocates sometimes cite the parallel of scholars who worked under other conquerors - Roman, Sassanid, Umayyad - whose institutional violence did not delegitimize the learning they sponsored.

The most contested element of this viewpoint concerns Tusi's role in the fall of Baghdad and the death of the Abbasid Caliph al-Musta'sim. Some accounts, including hostile medieval ones, portray Tusi as having advised Hulagu to proceed with the attack and as having provided justification for killing the caliph. Holders of the Mongol Service viewpoint either dispute these accounts as polemical fabrication by Sunni sources hostile to Tusi's Shia sympathies, or argue that even if accurate, Tusi had no capacity to prevent the conquest and that providing counsel to limit rather than inflame Mongol destructiveness was the most a scholar in his position could accomplish. They note that Hulagu needed no Persian astronomer's permission to sack a city he had already decided to sack.

Tusi's reputation during his lifetime and immediately after was split along confessional lines. Shia scholars generally treated him as a legitimate court scholar and theologian; Sunni sources were often hostile, linking him causally to the destruction of the caliphate. The rehabilitative reading of his Mongol service developed substantially in the twentieth century alongside the historiography of Islamic science. Scholars tracing the transmission of astronomical models from Maragha to Renaissance Europe found in Tusi a figure whose collaboration with the Mongols had, on any reasonable accounting, produced more for the continuity of human knowledge than it had cost. This genealogy - Maragha to Copernicus - became the primary lens through which the sympathetic interpretation of Tusi's choices was argued. Works by scholars debating his role in the fall of Baghdad have sharpened but not resolved the question of his specific agency.

Aydin Sayili - Turkish historian of science whose foundational study The Observatory in Islam (1960) framed Maragha as a major institutional achievement and treated Tusi's role under Mongol patronage as a practical success story for the preservation of learning.

George Saliba - Columbia University historian of Arabic and Islamic science, whose work on the Maragha school and its influence on Copernican astronomy is the primary modern scholarly basis for the high estimation of Tusi's scientific legacy. Saliba's Islamic Science and the Making of the European Renaissance (2007) is the central text in this lineage.

F. Jamil Ragep - McGill University historian of Islamic astronomy, editor and translator of Tusi's Tadhkira fi 'ilm al-hay'a. Ragep's scholarship treats Tusi as a towering figure whose institutional accomplishments under Mongol patronage represent a net gain for civilization, whatever the moral complexities of his position.

Seyyed Hossein Nasr - Iranian philosopher and historian of Islamic science whose biographical and philosophical treatment of Tusi, particularly in An Introduction to Islamic Cosmological Doctrines (1964), presents him as an exemplar of the Islamic intellectual tradition who navigated a catastrophic political rupture with his life's work intact.

Holders of this viewpoint disagree on several subsidiary questions:

• Degree of agency: Some argue Tusi was essentially a captive throughout - first at Alamut, then under Hulagu - and that the language of “collaboration” is anachronistic or misapplied. Others accept that Tusi exercised real choices and defend those choices on their merits rather than excusing them as coerced.
• The Baghdad role: The question of whether Tusi actively advised the killing of al-Musta'sim is disputed even among those sympathetic to his legacy. Some accept a version of the account and defend it as the act of a man navigating impossible circumstances; others reject the account as sectarian fabrication.
• Scope of the defense: Some proponents offer a full moral defense of Tusi's choices; others offer only a historical-contextual account that declines to adjudicate moral responsibility, arguing that judging a thirteenth-century scholar by modern standards of political ethics is anachronistic.

• Nasir al-Din al-Tusi - Main Topic
• Nasir al-Din al-Tusi - History
• Nasir al-Din al-Tusi - Mongol Service Debate
• Nasir al-Din al-Tusi - Traitor Viewpoint
• Maragha Observatory
• Fall of Baghdad (1258)
• Islamic Science - History
• Mongol Il-Khanate - History

1. Sayili, Aydin. The Observatory in Islam and Its Place in the General History of the Observatory. Ankara: Turkish Historical Society, 1960.
2. Saliba, George. Islamic Science and the Making of the European Renaissance. Cambridge, MA: MIT Press, 2007.
3. Ragep, F. Jamil, ed. and trans. Nasir al-Din al-Tusi's Memoir on Astronomy (al-Tadhkira fi 'ilm al-hay'a). 2 vols. New York: Springer, 1993.
4. Nasr, Seyyed Hossein. An Introduction to Islamic Cosmological Doctrines. Cambridge, MA: Harvard University Press, 1964.
5. Daftary, Farhad. The Isma'ilis: Their History and Doctrines. 2nd ed. Cambridge: Cambridge University Press, 2007. (On Tusi's captivity at Alamut.)
6. Neugebauer, Otto. “On the Planetary Theory of Copernicus.” Vistas in Astronomy 10 (1968): 89-103. (On Copernican planetary models; for the transmission argument, see Saliba.)
7. Lane, George. Early Mongol Rule in Thirteenth-Century Iran: A Persian Renaissance. London: RoutledgeCurzon, 2003.