We say the names of the days of the week constantly, but for most of us they are nonsense syllables. The seven-day system we use is based on the ancient astrological notion that the seven celestial bodies (the sun, the moon, Mars, Mercury, Jupiter, Venus, and Saturn) revolving around stationary Earth influence what happens on it and that each of these celestial bodies controls the first hour of the day named after it. This system was brought into Hellenistic Egypt from Mesopotamia, where astrology had been practiced for millenniums and where seven had always been a propitious number. In a.d. 321 the Emperor Constantine the Great grafted this astrological system onto the Roman calendar, made the first day of this new week a day of rest and worship for all, and imposed the following sequence and names to the days of the week: Di¶s S½lis, Sun’s Day; Di¶s L¿nae, Moon’s Day; Di¶s Martis, Mars’s Day; Di¶s Mercuriº, Mercury’s Day; Di¶s Iovis, Jove’s Day or Jupiter’s Day; Di¶s Veneris, Venus’s Day; and Di¶s Saturnº, Saturn’s Day. This new Roman system was adopted with modifications throughout most of western Europe: in the Germanic languages, such as Old English, the names of four of the Roman gods were converted into those of the corresponding Germanic gods. Therefore in Old English we have the following names (with their Modern English developments): Sunnandæg, Sunday; M½nandæg, Monday; Tºwesdæg, Tuesday (the god Tiu, like Mars, was a god of war); W½dnesdæg, Wednesday (the god Woden, like Mercury, was quick and eloquent); Thunresdæg, Thursday (the god Thunor in Old English or Thor in Old Norse, like Jupiter, was lord of the sky; Old Norse Th½rsdagr influenced the English form); Frºgedæg, Friday (the goddess Frigg, like Venus, was the goddess of love); and Saeternesdæg, Saturday.