Historical dates

Passages preserves your original date text. The date display uses a proleptic Gregorian calendar for display coordinates: Gregorian month lengths and leap-year rules extend backward before the calendar's historical adoption. This is a plotting convention, not a claim about which calendar a source used. Passages does not convert Julian dates, regnal years, dual years, or other historical calendar systems. Keep that wording and its citation; ambiguous entries remain accessible without a plotted position.

Enter a year (1512), a month (October 1512 or 1512-10), or a complete date (12 October 1512, October 12, 1512, or 1512-10-12). Unlabelled years use CE. Use BC/BCE or AD/CE explicitly for eras. There is no public year zero: 1 BCE is immediately followed by 1 CE.

The date engine retains precision separately from position. A month or year represents that whole calendar period; its display anchor is the midpoint, not an asserted day. Complete dates have day precision. Day coordinates do not depend on browser time zone. Invalid days and ambiguous numeric dates such as 03/04/1512 are not guessed.

A range such as 1512–1514 defaults to a possible-date interval. It does not assert that an event lasted that long. Choose Duration explicitly to represent an event lasting between the endpoints. An end date before the start remains unplaced with an explanation. A shared trailing era applies to both endpoints (44–42 BCE). Centuries represent the complete conventional period: the 15th century is 1401–1500, and the first century BCE is 100–1 BCE.

Circa, question marks, early, mid, and late remain qualifiers without invented numerical error margins. Before, after, by, and until are open bounds, not exact dates. Dashed spans distinguish these bounds from durations. Unknown or unsupported dates stay in the accessible unplaced section and exports.