Why our dates are ranges

Most history sites print one date and move on. We print the span the evidence actually allows, and we show you the evidence. Here is why.

Nobody wrote the date down

For almost everything that happened before the last two hundred years, no clock and no calendar page survives from the moment itself. What survives is clues: a king who was still alive, a census that was taken, an eclipse someone remembered, a building that had not been finished yet. Each clue rules something out. Put the clues together and you get a window: it cannot have been before this, it cannot have been after that. That window is the honest answer, and it is what we show.

A single date hides a decision

When a book says an event happened "in 5 BC", someone has quietly picked one year out of the window and thrown the rest away. You cannot see how wide the window was, which clue they trusted, or which clue they ignored. If a better clue turns up later, the single date is simply wrong, and nothing on the page tells you why. A range keeps the decision visible: here is the window, here is what made it this wide, judge for yourself.

How the bar works

Every event on this site carries up to four limits, worked out by the record store from what the sources say:

• Earliest it could have begun and latest it could have begun.
• Earliest it could have ended and latest it could have ended.

On the bar, a solid stretch means the event was certainly going on then; a hatched stretch means "somewhere in here". When the sources only say "sometime between A and B", the whole bar is hatched: we do not pretend to know more. An open end, with no limit at all, is marked as open rather than filled in with a guess.

Sources that disagree stay on the page

Often two good sources cannot both be right. We do not pick a winner and hide the loser. Each claim lists the sources that support it and the sources that contradict it, with the passage quoted, so the disagreement is part of the record. A reviewer may later mark a claim as supported or disputed, but even then the other side stays readable.

Years before year one

Dates before the year 1 are written "BC" (before Christ) on this site, because that is how people read them. In the machine-readable record they are written as astronomical years, where 1 BC is year 0 and 6 BC is −0005; that is the standard used by the Library of Congress's Extended Date/Time Format, and it lets the computer do arithmetic across the boundary without a gap. For dates before 15 October 1582 we show the Julian calendar, the one in use at the time; after that, the Gregorian calendar we use today.

Nothing is ever erased

A record on this site is never edited in place. A correction is a new version, with a reason, and the old version stays readable under "record history". If a date range narrows because a new source was found, you will see both the old range and the new one, and what changed between them. That is also how we keep ourselves honest: every number on the site can be traced to the version that produced it.

A worked example

Birth of Jesus of Nazareth. Sometime between 6 BC and 4 BC. Not earlier, not later; the sources do not narrow it further. Open the record to see the clues that set each edge of the window and the sources that argue about it.

Where this comes from

Everything on History Snippet is read live from Chronum, an open historical record store with an append-only database: rows are added, never changed or deleted. The time model follows the museum standard (CIDOC Conceptual Reference Model, time-span properties P82a, P81a, P81b, P82b). Anyone can read the same records we show here.