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Make a BC and AD Timeline

A BC and AD timeline shows events on both sides of year 1, such as the rise of Rome and the fall of its western empire, or the pharaohs of Egypt next to the Roman emperors. The two eras count years in opposite directions, which is what makes these timelines tricky to draw by hand. This article explains how the numbering works and how to build one in Preceden, which places BC and AD dates on the same axis for you.

How BC and AD years count

AD years count up from year 1: 1 AD, 2 AD, and so on to today. BC years count down toward year 1: 500 BC comes before 400 BC, and 44 BC comes before 43 BC. So on a timeline, BC years get smaller as you move right, until they reach 1 BC, and then AD years start growing from 1 AD.

A few rules keep the numbering straight:

  • There is no year zero. The year after 1 BC is 1 AD. So from 10 BC to 10 AD is 19 years, not 20.
  • Centuries follow the same pattern. The 1st century BC is the years 100 BC to 1 BC, and the 1st century AD is 1 AD to 100 AD. The 5th century BC covers 500 BC to 401 BC.
  • BCE and CE are the same years. BCE (Before Common Era) and CE (Common Era) are neutral names for BC and AD. 753 BCE and 753 BC are the same year, so use whichever your teacher or style guide prefers.
  • AD usually goes before the year and BC after it in formal writing (AD 79, 44 BC), but writing both after the year (79 AD, 44 BC) is common and easy to read.

Enter BC and AD dates

In Preceden, type a BC date the way you would write it, with the era after the year: 44 BC, 753 BCE and 3100 B.C. all work. Preceden accepts dates as far back as 240,000 BC, and a negative year such as -500 is saved as 500 BC.

You can add a month and day when you know them, as in March 15, 44 BC. For most ancient events a year is all the sources give, and a year on its own is fine.

For an event that covers a period, such as a reign, the start date is the larger BC year: Alexander the Great ruled from 336 BC to 323 BC. Add the era to both dates. An end date typed as 323 is read as 323 AD, so the event saves with a bar more than 600 years long. If the dates are the wrong way round, as in 323 BC to 336 BC, Preceden will not save the event and says the end date must be after the start date.

Three things are worth knowing:

  • Add AD to years 1 to 99. Preceden reads a bare two-digit year like 79 as 1979, so type 79 AD for the eruption of Vesuvius. Years from 100 onward need no era.
  • Type ancient dates rather than picking them. The calendar picker in the event dialog cannot show BC dates or years 1 to 99 AD, so type those dates straight into the date field.
  • Change BC dates in the event dialog. You can drag a BC event up or down to reorder it, but drag and drop cannot move it left or right or stretch its bar, so edit the dates instead.

Supported Date Formats lists every era marker Preceden recognizes, including the ones used in other languages.

How the timeline shows the eras

Preceden draws BC and AD events on one continuous axis, with the oldest on the left. The axis labels BC years with BC and AD years below 1000 with AD, so a timeline running from 500 BC to 500 AD reads clearly on both sides of the divide.

Each event keeps the era marker you typed while the event date format is Unformatted, the default. If you type 753 BCE, the event shows 753 BCE even though the axis says BC. For events that should read the same way whatever was typed, pick another format under Appearance > Date Formats.

For a span of several centuries, Preceden usually picks a suitable scale on its own. To set it yourself, open Appearance > Scale and choose units such as Centuries or Millennia.

Uncertain dates

Many ancient dates are estimates. When a source says "around 2600 BC", enter 2600 BC and check Approx. next to the date in the event dialog. Preceden then fades that end of the event's bar, and a single-date event reads Approx. 2600 BC, so readers can tell estimates from the dates you are sure of. Add or Update Timeline Event covers the details.

When historians disagree, pick one date for the timeline and mention the other in the event's notes.

Compare civilizations side by side

A BC and AD timeline often covers several civilizations at once. Put each one on its own layer, such as Egypt, Greece and Rome, and give each ruler or period an end date so it is drawn as a bar. The bars then show which civilizations overlapped and for how long. Make a Comparative Timeline walks through that approach, and Timeline Projects for School covers turning it into a class assignment.

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