Baghdad, the round city on the Tigris, is the richest city on earth. Caliph al-Ma'mun pays translators to turn Greek, Persian and Indian books into Arabic, and gathers scholars in his House of Wisdom. Here a mathematician from Khwarazm, Muhammad ibn Musa al-Khwarizmi, is finishing a book on solving equations. Its title gives us the word algebra. His own name becomes algorithm. The words are imagined.