The digits you are reading right now took a thousand-year road trip. India's decimal place-value system is documented across an area "roughly of the size of Europe" — the subcontinent to Cambodia — by about 600 CE. Arabic mathematicians adopted it in the 8th century, and al-Khwārizmī's textbook on Hindu reckoning gave Europe the word "algorithm." Europeans themselves held out longest: popular almanacs of 1557–96 still printed their dates in Roman numerals. Zero through nine conquered the world at walking pace.