How the Days of the Week Received Their Names

We have all doubtlessly wondered at some point how the days of the week received their names. Most of us probably have some vague recollection that the names have something to do with ancient Germanic deities. That is true, but the origins of the names for the days of the week actually go back even further than that. As a bizarre as it may sound, the story actually begins with ancient Babylonian astrologers.

The first people to develop a calendar with weeks consisting of seven days were the ancient Babylonians. Each day of the Babylonian week was associated with one of the seven celestial bodies that are visible with the naked eye.

The ancient Babylonians believed that each of these celestial bodies was one of their gods. The sun was believed to be Shamash, the god of law and justice. The moon was Sin. Mars was Nergal, the god of death and plague. Mercury was Nabu, the god of knowledge, wisdom, writing, and messengers. Jupiter was believed to be Marduk, the national god of the Babylonians. Venus was Ishtar, the goddess of love, beauty, sex, war, violence, and political power.

ABOVE: Ancient Babylonian astronomical tablet recording the movements of the planet Venus over the course of twenty-four years

During the Hellenistic Period, ancient Greek astrologers became fascinated by the writings of their Babylonian forebears and created their own version of the Babylonian seven-day week, only they substituted the names of their equivalent deities in place of the Babylonian names. Thus, the seven days of the Greek astrological “week” were: ἡμέρᾱ Ἡλίου (day of Helios), ἡμέρᾱ Σελήνης (day of Selene), ἡμέρᾱ Ἄρεως (day of Ares), ἡμέρᾱ Ἑρμοῦ (day of Hermes), ἡμέρᾱ Διός (day of Zeus), ἡμέρᾱ Ἀφροδῑ́της (day of Aphrodite), and, lastly, ἡμέρᾱ Κρόνου (day of Kronos). These days were only known by astrologers and were not used by everyday people.

Meanwhile, in Italy, the ancient Romans used an eight-day week to keep track of time. The first seven days of the Roman week were devoted to labor, but, on the eighth day, everyone was allowed to take time away from work in order to go shopping and buy supplies for the coming days. The purpose of this system was purely pragmatic; it allotting a specific time for commerce, thereby allowing all other days to be devoted to labor. The days did not even have names; instead, each day was merely signified by a letter: A, B, C, D, E, F, G, and H.

Then, after the Roman Empire annexed Greece, the system began to shift. The traditional Roman eight-day week began to be replaced with a seven-day week in the same style of the Greek astrological one. The Romans, of course, renamed all the days on their calendar after the deities in their own pantheon, whom they saw as being equivalent to the Greek deities. Thus, the days of the week became: dies Solis (day of Sol), dies Lunae (day of Luna), dies Martis (day of Mars), dies Mercurii (day of Mercurius), dies Iovis (day of Iove), dies Veneris (day of Venus), and dies Saturni (day of Saturnus). The last of these days, dies Saturni, became the new day devoted to trade and commerce.

At some point, the Romans came in contact with the Germanic peoples. In effort to emulate the glory of imperial Rome, the Germanic tribes adopted the Roman-style seven-day week, but they renamed the days after their own deities, whom they syncretized with the Roman ones. Among these Germanic tribes were the Anglo-Saxons, the people who would later become the English.

The seven days of the Anglo-Saxon week were: Sunnandæg (day of Sunne), Mōnandæg (day of Mōna), Tīwesdæg (day of Tīw), Wōdnesdæg (day of Wōden), Þunresdæg (day of Þunor), Frīgedæg (day of Frige), and Sæternesdæg (day of Saturn). These seven days later became corrupted into the seven days of week that we know today: Sunday, Monday, Tuesday, Wednesday, Thursday, Friday, and Saturday.

At this point, you are probably thinking “Wait! What about the whole thing in the Bible about the seven days of the week representing the seven days of creation?” This is where things become really complicated. In 587 or 586 B.C., under the leadership of Nebuchadnezzar II, the Babylonians burned the city of Jerusalem to the ground and took thousands of Jewish captives to Babylon, including a large number of Levitical priests.

ABOVE: The Flight of the Prisoners (c. 1896-1902) by James Tissot

The creation story found in Genesis 1:1-2:4a is believed by modern scholars to have been written by a group of those priests living in Babylon during the Babylonian Exile. For this reason, it is generally believed that the writers of the Old Testament probably received the idea of a seven-day week from the Babylonians. It is also possible, however, that the Hebrews and Babylonians, who both spoke Semitic languages, may have both derived the concept from an even earlier Proto-Semitic source.

For the ancient Israelites, the only day of the week that had a name was the seventh day: the Sabbath. When Christianity became the dominant religion of the Roman Empire, dies Saturni, the traditional Roman day of commerce, was syncretized with the Jewish Sabbath. Thus, it was no longer a day for shopping, but instead a day of rest.

The reason why church services are not held on Saturdays is because early Christians sought to segregate themselves from the Jews. The Didache, a first-century A.D. Christian catechism, warns believers:

But let not your fasts be with the hypocrites, for they fast on the second and fifth day of the week. Rather, fast on the fourth day and the Preparation.

Although they mostly agreed that they should not hold their services on the Sabbath, early Christians disagreed on which day they should hold their services on. Church services in different towns were often held on different days. Both Sunday and Friday were popular days for worship services.

ABOVE: Ancient Roman silver disk from the third century A.D. depicting the sun god Sol Invictus

In the fifth century A.D., this began to change. In his early years, Emperor Constantine was a devotee of the sun god Sol Invictus. After his victory in the famous Battle of Milvian Bridge, he chose the Christian God as his new personal deity. As a sign of the Christian God’s superiority over Sol Invictus, Constantine renamed dies Solis as dies Domini, meaning “day of the Lord.” This renaming is still followed in the romance languages today. In English, however, the old pagan name continues to be used.

The English names of the days of the week have been challenged many times, but they have never been successfully changed. In the seventeenth and eighteenth centuries, the Quakers attempted to rename the days of the week after numbers, calling them: “First Day,” “Second Day,” “Third Day,” and so on. By the late 1800s, they had largely abandoned this effort because they realized that, even though the days of the week were originally named after pagan deities, those ancient deities were all long forgotten.