Historians map ancient borders by piecing together written sources, inscriptions, milestones and archaeology, then drawing a best estimate. Ancient states rarely had surveyed lines, so every outline is a judgement, and our map says how each one was made.
Key takeaways
- Roman frontiers were zones with roads, forts and rivers, not lines, so any border drawn today is an estimate.
- Our map has 13 key dates, and each outline is made by one of four stated methods.
- Only AD 117 and AD 211 use the Ancient World Mapping Center outline directly.
- Every year page says how its outline was made, so you can judge how far to trust it.
How borders on an ancient map are made
The homepage explains in three short reasons why the borders are approximate: frontiers were zones, client kingdoms are a judgement call, and many dates are rebuilt. This page goes behind that and shows how a mapmaker actually gets from evidence to an outline.
Historians work from several kinds of evidence. Ancient writers describe campaigns and provinces. Inscriptions and milestones show where Roman officials and roads reached. Archaeology finds forts, towns and boundary stones. None of it comes as a line, so the mapmaker joins the dots. Where the evidence is thin, they have to choose.
The Ancient World Mapping Center (AWMC) at the University of North Carolina is one of the main sources for this kind of work [1]. It publishes its geospatial data for the ancient world as open GeoJSON files, covering things such as roads, regional names, coastlines and rivers. The data derives from the Barrington Atlas of the Greek and Roman World and is shared under the ODC Open Database Licence [2]. Places come from a separate project, the Pleiades gazetteer [3], which has its own entry in our Pleiades gazetteer page.
AWMC says it aims for highly accurate data and will keep refining older files [2]. That is a stated aim, not a guarantee, which is why we describe our outlines as estimates.
An example from our data
Our map has 13 key dates, and each outline is made by one of four methods. The method is a fact on every year page.
- A symbolic circle. For 753 BC, the outline is a symbolic circle around the city, since nothing like a border existed.
- The Ancient World Mapping Center outline. AD 117 and AD 211 use the Ancient World Mapping Center outline directly. At the first, the empire covers 4.88 million km².
- Rebuilt from the provinces Rome held. 133 BC, 44 BC, AD 14, AD 395, AD 476 and AD 565 use the provinces Rome held, drawing them from the AD 200 province outlines.
- Modern regions. 264 BC, AD 1000, AD 1180 and AD 1453 follow modern regions, so they are the coarsest.
The practical lesson is that a size quoted for one date is not strictly comparable with the next. The peak in AD 117 is 4.88 million km² on our map, and other sources give different figures because they treat client kingdoms and desert edges differently.
The thing people get wrong
Most people think there is a "true" map of the Roman Empire out there and that a good map just reproduces it. In fact a Roman frontier was a zone with troops, roads and trade across it, and which client kingdoms to count is a choice. Two careful historians can draw different outlines from the same evidence, and both can be defensible. The honest approach is to say how the line was drawn, as our year pages do.
Frequently asked questions
Did the Roman Empire have a border line?
Not in the modern sense. Frontiers were zones, often marked by rivers, roads, forts or walls, with trade and travel crossing them.
Where does the map's border data come from?
From the Ancient World Mapping Center at the University of North Carolina, for the dates with detailed outlines. Other dates are rebuilt from the provinces Rome held, or follow modern regions.
Why do different maps show different sizes?
Because they make different choices about client kingdoms and frontier zones, and some dates are rebuilt rather than surveyed.
Sources
- Ancient World Mapping Center, University of North Carolina.
- AWMC geodata, Ancient World Mapping Center (GitHub).
- Pleiades, Pleiades (Institute for the Study of the Ancient World and others).
- Every figure from our own map is worked out from the datasets on the data sources page (checked against Ancient World Mapping Center outlines and Pleiades).