Mind-Benders of Islamic History
A mathematician in Baghdad while Charlemagne ruled Europe
Al-Khwarizmi — the Baghdad mathematician whose Latinized name gave English the word “algorithm” — was born around 780, while Charlemagne was building his empire across Europe (he was crowned emperor in 800). The Hindu-Arabic calculating methods al-Khwarizmi helped systematize would not take firm hold in Latin Europe until Leonardo of Pisa (Fibonacci) championed them in his Liber Abaci of 1202, nearly four centuries later.
How we know
al-Khwarizmi c.780–850 CE (algebra treatise compiled 813–833, Baghdad House of Wisdom); Charlemagne 748–814, crowned emperor 800; Fibonacci's Liber Abaci 1202. Overlap 780–814 = 34 yrs; 1202 − c.820 = 382 yrs (~4 centuries).
One of many fact-checked wonders across eight traditions at The Spring of Wisdom.