When were the days of the week named?

The names of the days of the week have their origins in ancient cultures, primarily derived from the Roman and Germanic traditions. The Romans named the days after their gods and celestial bodies, with Sunday dedicated to the Sun and Monday to the Moon, among others. This system was later adopted and adapted by the Germanic peoples, who associated the days with their own deities. The seven-day week as we know it became widely established by the 4th century AD, largely due to the influence of Christianity and the Roman Empire.