Reading the dates in this atlas
Every profile in this atlas prints two date lines - a birth line and a death line - and they are not all written to the same precision. Some give a day, a month and a place. Some give a bare year. Some open with a tilde or a c. Two print the same day twice under different calendars. The short answer: the qualifier is the honest part. A tilde or a c. means the year is a scholarly estimate, not a record; a bare year means the year is attested but the day is not; (OS) and (NS) mean the date exists in two calendars and both are shown rather than one being quietly picked.
Underneath the printed line, each figure also carries a single whole number for birth and a single whole number for death. That number is what the timeline and the chronological sort run on, and it is the place where all of that nuance is thrown away. Knowing which figures have a soft number is the difference between reading the timeline as a chronology and reading it as a measurement.
The six date forms used in the atlas
Across the 125 profiles the birth line takes six forms. The table below counts them, and every form is a deliberate signal about how much is actually known.
The counts matter because they tell you how much of the atlas is firm. Eighty of the 125 birth lines carry a day and a month, which is the signature of a documented record - a parish register, a court record, a newspaper. Forty-one carry something less than that.
| Form | Birth lines | Example | What it means |
|---|---|---|---|
| Day and month | 80 | Julius Caesar: 12 July 100 BCE, Rome | A date that survives in a source, to the day |
| Approximate, ~ or c. | 24 | Hannibal Barca: c. 247 BCE, Carthage | Scholarly estimate, usually from an age given at death or at an event |
| Year only | 16 | Aristotle: 384 BCE, Stagira, Chalcidice | The year is attested, the day is not recorded |
| Two calendars | 2 | Isaac Newton: 25 December 1642 (OS) / 4 January 1643 (NS) | The day exists in both the Julian and the Gregorian reckoning |
| Baptism, not birth | 2 | Adam Smith: Baptized 16 June 1723, Kirkcaldy | The church register survives; the birth itself was never written down |
| Century only | 1 | Homer: ~8th century BCE, Ionia | Not datable to a year by any surviving evidence |
Why BCE years run backwards, and why there is no year 0
BCE means Before Common Era and CE means Common Era. They number the same years as BC and AD and they start from the same point; only the labels differ. The practical consequence is the one that catches readers out: BCE years count down. 753 BCE is earlier than 146 BCE, and a figure born in 100 BCE who died in 44 BCE lived 56 years, not minus 56.
There is also no year 0. The year before 1 CE is 1 BCE. That makes any span that crosses the divide one year shorter than subtraction suggests, and this atlas is a worked example of the trap. The earliest birth year it holds is 750 BCE (Homer) and the latest death year is 2005 (Rosa Parks). Subtract the two numbers and you get 2,755. The elapsed span is 2,754 years, because the arithmetic counted a year 0 that never existed.
Three figures in the atlas live across the divide, and their profiles are where you can see the convention working: Augustus (23 September 63 BCE to 19 August 14 CE), Ovid (20 March 43 BCE to c. 17/18 CE) and Seneca the Younger (c. 4 BCE to 65 CE). Twenty-four of the 125 figures were born BCE and 21 died BCE.
What a tilde or a c. is actually telling you
Twenty-four birth lines open with ~ or c. - circa. Both mean the same thing here: the year is an inference. For most of the ancient figures it is inferred from a secondary statement in a later source, often an age at death or a year relative to a known event. Socrates is given as ~470 BCE to 399 BCE: the death year is firm, because his trial and execution in Athens are dated events, while the birth year is reconstructed from the age he is said to have been at the trial.
The qualifier can also sit on the death line. Sappho is given as ~630 BCE to ~570 BCE (uncertain), and Euclid as ~265 BCE (uncertain; Alexandria). Where a profile says uncertain in words as well as in the symbol, that is a flag that scholarship does not agree, not a rounding note.
Two profiles state their uncertainty in a way worth recognising. Christopher Columbus is given as between August 25 and October 31, 1451 - a window rather than a date, which is what the Genoese documents support. And Homer is dated only to the 8th century BCE, because nothing survives that would narrow it; the atlas assigns him the years 750 and 700 so that he can be placed on the timeline at all, and those two numbers are the softest in the corpus.
(OS) and (NS): the same day in two calendars
Old Style and New Style mark the Julian and the Gregorian calendar. The Gregorian reform of 1582 was adopted immediately in Catholic Europe and only in 1752 in Britain and its colonies, so for 170 years a date in London and a date in Rome were not the same day even when they were written identically.
Isaac Newton is the clean example. His birth is printed as 25 December 1642 (OS) / 4 January 1643 (NS). Both are correct: the English parish record says December 1642, and the equivalent Gregorian date, ten days later in the seventeenth century, falls in the following January. Notice what the atlas does with the single sort number - it stores 1643, the New Style year. He is placed in the Scientific Revolution & Enlightenment era by a number that does not match the year printed first on his own page.
Thomas Jefferson carries only the New Style date, 13 April 1743 (NS), and the tag is there precisely so you do not read it as an unqualified Julian date. The sharpest case in the atlas is a pair. William Shakespeare died on April 23, 1616 in Stratford-upon-Avon; Miguel de Cervantes is given as April 22, 1616 in Madrid. A relationship note on Shakespeare's profile takes up the familiar line that the two died on the same date, and corrects it with the crucial qualifier - different calendars. That qualifier is the whole story: England was still Julian in 1616 and Castile had been Gregorian since 1582, so an English April 23 and a Spanish April 22 are not one day apart but about a week and a half. The two men did not die on the same day, and the two date lines on this site are not in the same calendar even though they are written in the same format.
The practical rule when you are comparing early-modern lives across Europe: check whether both dates are in the same style before you call two people contemporaries to the week. To the year, the atlas is reliable. To the day, across 1582-1752, it depends on which capital the record was kept in.
Baptism dates, and why they are not birth dates
Two profiles print a baptism rather than a birth. William Shakespeare is given as April 26, 1564 (baptized) and Adam Smith as Baptized 16 June 1723. In both cases the parish register is the only surviving document and it records the sacrament, not the delivery.
This is one of the most common silent errors in popular history writing: a baptism date quoted as a birthday. The atlas keeps the word baptized in the line so the distinction survives. Where you see it, read the date as an upper bound - the birth came days, occasionally weeks, earlier.
How the single sort number is used
Alongside the printed date lines, each figure carries one integer for birth and one for death, with BCE years stored as negatives. Three features of the site run on those integers rather than on the prose: the chronological timeline, which orders all 125 figures by birth year and breaks ties alphabetically; the century dividers along it; and the era assignment on every profile.
The timeline prints those integers using a plain rule: a negative year becomes N BCE and a positive year becomes N CE. That is why Archimedes shows as 287 BCE on the timeline while his profile's birth line reads ~287 BCE - the symbol does not survive the conversion to a number.
So the timeline is best read as an ordering, not a measurement. For the 80 figures with a day-precise birth it is as accurate as the sources. For the 41 with an approximate or partial date it is a placement decision, and for Homer it is frankly a convention.
- Firm: any figure whose birth line carries a day and a month.
- Firm year, soft day: a bare year, such as Marco Polo, 1254 CE, Venice.
- Soft year: anything with ~ or c., including most of Ancient Greece and several medieval figures such as Joan of Arc, c. 1412.
- Convention only: Homer, dated to a century and placed at 750 BCE.
Reading a date line in practice
Take Hannibal Barca: c. 247 BCE, Carthage to c. 183 BCE, Libyssa, Bithynia. Four things are being said at once. The years are estimates, not records. He died outside the city he was born in, and both places are on his profile because the atlas associates figures with cities as well as eras - Carthage is listed as near modern Tunis. He belongs to The Roman World rather than to a Carthaginian era, because this atlas periodises the West by the political system that dominated the Mediterranean, not by the subject's own loyalties. And his sixty-four years are a subtraction of two soft numbers.
None of that makes the profile unreliable. It makes it a summary with its precision marked, which is what a reference page should be. If a date matters for your purpose - a citation, an argument, an exam answer - the qualifier tells you whether you can lean on it or need to go to the scholarship.
Questions readers ask
What is the difference between BCE and BC?
None in the numbering. BCE/CE and BC/AD mark the same years from the same starting point; BCE and CE are the forms now standard in academic writing because they do not embed a religious claim in the label. This atlas uses BCE and CE throughout, including on the timeline, where a stored negative year is printed as N BCE.
Why does one profile show two different birth years for the same person?
Because the date exists in two calendars. Isaac Newton was born on 25 December 1642 by the Julian calendar England still used, which is 4 January 1643 by the Gregorian calendar most of Europe had already adopted. Both are printed. The atlas sorts him by 1643.
Does c. mean the date is wrong?
No - it means it is an estimate rather than a record, and that the estimate is the best scholarship offers. Twenty-four of the 125 birth lines carry ~ or c. For ancient figures this is normal: the year is usually reconstructed from an age reported at death or from a position relative to a dated event.
Can I trust the timeline for exact gaps between two lives?
Treat it as an ordering. It runs on one whole number per birth and death, so it is exact for the 80 day-precise figures and approximate for the rest. It also counts arithmetically across the BCE/CE divide, which overstates any span crossing it by one year, because there is no year 0.
Why is a baptism date shown instead of a birth date?
Because that is the document that survives. For William Shakespeare and Adam Smith the parish register records the baptism and nothing records the birth. The word baptized is kept in the line so the date is not read as a birthday; the birth was earlier.
Where this comes from
Every count in this guide is derived from the atlas data itself rather than written by hand, so the prose cannot drift from the corpus. The profiles are researched editorial summaries, not primary sources: what a figure profile contains - and what it does not sets out exactly which fields exist and where they stop.