I'd always thought (though I don't have a specific source I can recall), that the seven days of the week was drawn from the seven non-fixed celestial bodies vis

I'd always thought (though I don't have a specific source I can recall), that the seven days of the week was drawn from the seven non-fixed celestial bodies visible ot the naked eye: the Sun, the Moon, Mercury, Venus, Mars, Jupiter and Saturn. The planets were frequently associated with and named after deities, so the days of the week also have the names of deities.