Let's explore a bit about weekdays, and where that rainbow comes from
What Day Is Today?
Weekdays are a surprisingly mundane but ubiquitous concept, pretty much all across the world, our days are grouped into sevens, if we're particularly culturally connected, the seventh (or the first depending on how you keep up count) is going to be named after the Sun. A bit of an important persona when it comes to life on this little ball of wonder no doubt. In any case, today (when I am writing) is actually a terribly long, mixed, dusty, angry, and upsetting Wednesday. Known to be quite the peak of the week (hence the special name Mittwoch in German), I was having a bit of a terrible wednesday. And thus begins the train of thought, because that is what man - being a thinking animal - does best. Thinks!
Roman Roots
Turns out the days of the week much like several other concepts actually come from the Romans. Being the great civilised people they are, Romans much like their other civilised contemporaries required a way to track the passing of days. It is from the Romans that we get our first idea of modern days, one for their gods, Eg: one for Jupiter, one for Mercury, one for Mars, and so on...
However that begs a very important question, why it today the -day it is, as in has everyone been following the same basic sequence of days since time immemorial, if so who put up a marker and said today's sunday and started the week.
Daying the Date
Origin Backstory
The earliest dayed date we know comes from a rather quaint and well preserved mountainside town south of Rome, near what is today the city of Napoli (Naples to an english audience) where a quaint late August (date contested) was about to take a decidedly unquaint turn. In Pompeii in 79CE, the mountain the city was build next to, Mt. Vesuvius, was at the precipice of an eruption of great historical significance. And in late August, it the bubbling magma inside the earth forced itself (along with large volumes of ejecta) outside the peak, forming a great black cloud (not dissimilar to a mushroom cloud) around the mountain. A cloud which descended in a deadly rain of very hot ash and stone. A combination of magma, very hot mud, and rocks then started to make it's way down the mountain. If you were caught in the flow or this hellish earth, you could count yourself lucky, since the flow is hot enough to cause instant death, for those who managed to barricade themselves, they would suffer a much more haranguing death, being quiet nearly baked alive, trapped.
Couple of days later, after this cataclysminc incident, when things would have quitened down, there would be almost nothing left of the city, nothing visible, perhaps a couple of structures poking above the mud, the suddenness of the flows means that a lot of the region got buried, and with a suddenness that lends itself well to preservation, and as a result, Pompeii is incredibly well preserved. A wealth of material from the era reaches us from Pompeii. In addition to material, another important thing that has been is graffiti, while lacking the usual gravitas, and dignitas of which the nobility of Rome are renowned for, the graffiti of Pompeii gives us a fantastic window into the lives of commoners in Rome. Examples include well wishes like:
Defecator, may everything turn out okay so that you can leave this place
To achievements,
Some of which were mundane
I made bread
or some less so,
Hic ego puellas multas futui
(I am not going to explain that)
Story Thickens
One of the many preserved graffitis from Pompei is a small text which reads:
Nerone Caesare Augusto Cosso Lentuol Cossil fil. Cos. VIII idus Febr(u)arius dies solis, luna XIIIIX nun(dinae) Cumis, V (idus Februarias) nun(dinae) Pompeis
Note the word nundinae, it is related and for a separate postworthy reason. However this statement also tells us something tantalising. In english this translates to:
"In the consulship of Nero Caesar Augustus and Cossus Lentulus, son of Cossus, on the eighth day before the Ides of February (February 6), day of the sun (Sunday). The lunar day was the 14th/19th. The market day (nundinae) was at Cumae, and on the fifth day before the Ides of February (February 9), the market day was at Pompeii".
We know when the consulship of Nero and Cossus was (AD 60), and thus we know the date that is referred to (February 6th) and the inscription says something very important dies solis, day of the Sun, i.e. Sunday. Thus making Sunday February 6th AD 60, the first know date in history with a day assigned to it, now to quickly verify....
Wait what!
The day is Wednesday, wth graffiti artist, not cool. However it turns out the graffiti artist is not all wrong, there's multiple ways to associate days with gods, one by the early hours of the day, and another by the later hours of the preceding day, and when we change our method of calculation, we get a Wednesday. So not all wrong, however incomplete.
Remember the word we mentioned, nundinae, these refer to market days. Ancient romans di not have a concept of a 7th day week, instead days were named after planets who ruled either the first hour of the day, or the last of the preceding one, and people used all sorts of different weeks, the 7 day week was not in yet.
The modern 7 day week comes from Jewish traditions, and to help date with that, we have the aid of an older inscription, one which says:
year 7 of Domitian Caesar … month of Tybi 25, 1st hour of the day, sambat 6
Not the sambat 6. The sixth day of Sabbath week. We know the 7th year of the Domitian Caesar (87 CE) and the date Tybi 25th corresponds to December 28th. A known friday. Thus making this day one of the earliest known Friday's in human history.