Mind-Benders of Islamic History
He built his observatory under the man who sacked Baghdad
The polymath Nasir al-Din al-Tusi (1201-1274) lived through the Mongol conquest of Baghdad in 1258. In the service of the Mongol ruler Hulagu Khan, he secured funding for a great observatory at Maragha, begun in 1259, which became one of the most advanced astronomical centers of its age.
How we know
Nasir al-Din al-Tusi 1201-1274; Mongol sack of Baghdad Feb 1258 (al-Tusi ~57); Maragha observatory construction begun 1259 under Hulagu Khan's patronage (MacTutor; Wikipedia, Maragheh observatory).
One of many fact-checked wonders across eight traditions at The Spring of Wisdom.