Four Days, Four Markets, and the Months They Build

The izu, the Igbo week, runs only four days, Eke, Orie, Afo and Nkwo, and the four names do double duty as the days on which a locality's principal markets are traditionally held in rotation, so towns across Igboland still carry the day names built into their own place names, an Eke market town or an Afor market town identifying itself by which day of the cycle its market falls on.

Traditional reckoning builds larger units from this four day base rather than borrowing a seven day week or a thirty day month from outside: seven izu make an onwa, a twenty eight day month tracking the moon closely enough to serve as a lunar proxy, and thirteen onwa make an afo, a year of roughly three hundred sixty four days. Each of the four days is bound to its own spirits and observances rather than being interchangeable, so the calendar carries a religious charge on every one of its four positions rather than concentrating ritual significance on a single sabbath-like day the way a seven day week often does. Igbo oral tradition, recorded in detail by early twentieth century ethnographers working directly with Igbo communities, holds that the four day week and its market-spirit associations were established through the religious authority of Nri, the priest kingship whose ritual influence historically extended across much of Igboland.