Names of the week

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Italian cameo bracelet representing the days of the week, corresponding to the planets as Roman gods: Diana as the Moon for Monday, Mars for Tuesday, Mercury for Wednesday, Jupiter for Thursday, Venus for Friday, Saturn for Saturday, and Apollo as the Sun for Sunday. Middle 19th century, Walters Art Museum: The names of the days of the week in many languages are derived from the names of the classical planets in Hellenistic astrology, which are in turn named after contemporary deities; a system introduced by the Roman Empire during Late Antiquity. In some other languages, the days are named after corresponding deities of the regional culture, either beginning with Sunday or with Monday. In the international standard ISO 8601, Monday is treated as the first day of the week.