So, I saw someone tweet out this photo:

“Sorry to burst everyone’s bubble, but there was NO year 0. We started with year 1, so the new decade is 2021.”

Yeah…not so much. I have a couple of problems with this.

I remember back in 1999 when everyone was saying things like this about the year 2000. That it’s not the start of the new millennium, so we should be celebrating until next year.

The logic is pretty straightforward. There was no year zero, so the first year was 1. Therefore the second year was 2, the third was 3, and so on…up until the 1000th year, which was numbered 1000. A millennium is 1000 years, and the first 1000 years — the *first millennium* — were numbered 1 to 1000. Therefore, the *second millennium* had to begin in the year 1001, and if you count that as the first of another 1000 years, then the second millennium had to end with the year 2000. Thus, the third millennium begins with the year 2001. The year 2000 was part of the previous millennium.

My first objection to the sign above is that we don’t number decades the way we number millennia. Nobody went out celebrating “the start of the 203rd decade.” What they celebrated was the start of the ’20s, which unsurprisingly start in 2020. We group years into decades differently than we do centuries or millennia: Decades start with the year ending in 0. That’s just how it is.

You could object that our decade groupings are wrong, but that brings me to my second problem. Everyone making this argument (including the sign maker above) likes to point out, “there was no year 0.” But you know what? The sign is wrong when it says we “started with year 1,” because there was no year 1 either. Nor a year 2 or year 3 or year 10. There wasn’t even a year 500.

The *anno Domini* system for labeling years wasn’t invented until the year 525. Actually, if I’ve done the math right, our current year numbering system was invented in the year 241 under the *anno Diocletiani* era, named after the Roman Emperor Diocletian and dated back to the first year of his reign. He was a persecutor of Christians, so this era was also known as the “Era of the Martyrs.”

Christian scholars weren’t terribly fond of numbering years based on the reign of an Emperor who persecuted them, so a monk named Dionysius Exiguus decided to change all that by numbering the years based on an era that started with a happier event for Christians: The birth of Jesus Christ. How exactly he determined that Christ had been born 525 years earlier is a little unclear. (Dionysius was fuzzy about his sources.)

Actually, despite the invention of *anno Domini* in 525, there wasn’t even a year 525 — Dionysius proposed that his new system should start after Diocletian 247 with *anno Domini* 532 replacing Diocletian 248. So 532 was the first year of our current calendar…for some people. Because the truth is that the *anno Domini* system wasn’t very popular until Emperor Charlemagne started using it sometime around the year 800. It didn’t spread to the rest of Europe until maybe the 1400s, and *anno Domini* didn’t become a world-wide standard until the development of modern trade and communications in the 1900s. Given all this history, it’s pretty clear we didn’t really “start with year 1.”

I suppose someone could argue that even though we started with year 532, it was still possible to *count back* to year 1, so it still makes sense to talk about counting decades, centuries, and millennia from year 1. But then we can also count back to year 0, and starting with year 0 makes all the decades, centuries, and millennia begin and end in years that are much more intuitive to most people.

So let’s just do that. Calendars and timekeeping are complex enough without making up pointless rules about arbitrary starting points.

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