A Straight Dope Classic from Cecil's Storehouse of Human Knowledge

What year numbering system was used in the time of Christ?

September 14, 1990

Dear Cecil:

Pretty soon we'll be starting a new decade (since, as all educated people realize, decades start with a one, not a zero). This got me wondering. AD 1991 means "in the year of our Lord 1991." [Ed. note: This question was originally published in 1990, but it has a certain continuing relevance.] When did this system start? I assume that after Christ was crucified, it wasn't just a matter of people saying, "Truly, he was the Son of God. Better renumber the calendar." What numbering system did Christ's contemporaries use?

Cecil replies:

Good question, Robster, but first let me congratulate you on getting the facts straight on the new decade not starting until the end of 1990, 2000, etc. When I pointed this out on New Year's Day, 1990, one woman cried out in anguish, "My God, you mean it's still the 80s?" She had my sympathy, but facts is facts.

The Christian system of year numbering was invented in what we now know as AD 525 by a monk named Dionysius Exiguus, who had been asked by the pope to work out a better way to figure when Easter occurred. There was probably a simpler way of doing this than renumbering the entire calendar, but I guess Dionysius got a little carried away. Surprisingly, considering the distinguished nature of the honoree, it took a while before the Anno Domini ("in the year of the Lord") method caught on. The popes didn't use it routinely until the 10th century AD and the Greeks didn't come around until the 14th century.

One defect of the calendar is that Dionysius miscalculated the date of Christ's birth. The somewhat incongruous result was that by modern calculation Christ was born about 4 BC — meaning Before Christ, of course. But we all make mistakes.

In Christ's time the Romans numbered their years anno urbis conditae, from the founding of the city [of Rome]. Christ was born circa 750 AUC. Other systems of reckoning were also used from time to time. One of the odder ones, in common use during the middle ages, was called the indiction. It was a rotating 15 year cycle — you got to 15, you started over again at 1. No doubt this bespeaks a rather static conception of history — none of this modern idea of progress, you know. But at least they weren't bothered by people getting nostalgic for the Sixties.

Battle of the decades

Dear Cecil:

It is extremely disappointing to find you spouting the line that the "0" year is the end of the decade. So let's get this straight: there is no such thing as "starting a new decade" — a decade is any ten years, and you can define it from May 25, 1985 to May 24, 1995 if you so desire. The "80s," however, is that decade every century during which the numeral "8" appears next-to-last in the year number. So don't try to be so much more clever than the rest of us all the time, OK?

Cecil replies:

I try not to be, Kenny, but sometimes it just happens. I assume we're agreed the next century starts on January 1, 2001, not January 1, 2000. (If not, there's no point continuing.) Call me wacky, but it seems only reasonable that the start of the new century and the start of the new decade ought to coincide. Granted there's no harm done if they don't. No harm if your socks don't match, either. But some people it bothers. Sorry if I'm such a fussbudget.

Battle of the decades, part two

Dear Cecil:

You fell into an ignorant trap trying to claim the '90s won't start until 1991. Let's take it from the top. The first decade AD started in the year 1; the second began in year 11. Time marched on. People acknowledged that the 5th century, the fifth set of 100 years since 1 AD, began in 401 AD, the 11th century in 1001, etcetera. But one day somebody started talking about, oh, the "1300s."

The same reasoning applies to decades. I will grant you that the 200th decade AD will not begin until 1991. But "decade" refers to a ten year period. Any ten year period. Webster's New Collegiate Dictionary defines the sixties as "the years 60 to 69 in a lifetime or century." If someone tells you they live in New York "in the East Sixties," you wouldn't expect them to live on 70th Street, would you? The '90s (and the 1900s) will end as the year 2000 begins. But the 20th century will still have a year to go.

Cecil replies:

Oh, piffle. There's no point being a columnist if you can't be obstinate in the face of all logic. If you're determined to stick to this silly idea that "the '80s" means all the years with eightysomething in their names, be my guest.

And now back to the battle of the centuries

Dear Cecil:

Your bland assumption that no intelligent being could possibly believe anything but that the second millennium of our era will begin on January 1, 2001, sent me into such a froth that I simply had to reply. Hence the enclosed.

Cecil replies:

Fun's fun, Chris, but a man's got to draw the line somewhere. The essay you enclose draws an analogy between the calendar and a mathematical number line. The starting point on the number line is zero; therefore, you opine, the starting point on the calendar should be the year zero. If that's so, 100 years will have elapsed on December 31 of the year 99, and 20 centuries will have gone by on December 31, 1999, making January 1, 2000 the start of the second millennium.

This argument is appealing but stupid. As we discussed in my first book, The Straight Dope (which appeared 15 years ago, for Pete's sake), the first year in the calendar is not zero but 1. The first century concludes December 31 in the year 100, the second millennium finishes up December 31, 2000, and the next century and millennium start January 1, 2001.

There is a host of logical counterarguments to be raised against the number line analogy, but never mind them. We need merely point to the example of history. On September 22, 1792, French revolutionaries declared a republic and, in the interest of doing a thorough job of sweeping out the old, decided to restart the calendar. Did they call the first year of their grand social experiments "the year zero"? Don't be silly. They proclaimed that "henceforth all public acts shall bear the date of the first year of the French Republic," Year I for short. Year I was followed by Year II, Year II by Year III — you see the pattern. I hope (but doubt) this will settle the question once and for all.

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