Data sources & licences

This site is built entirely on open data and open-source software. Thank you to everyone who collected, shared and maintains it. Here is exactly what we use and the licence each part comes with.

Data version

AWMC geodata commit 7ecf8bc (2024-04-22); Pleiades dump 20261011; Itiner-e 2024 1.3

Last refreshed

2026-10-13

Software

The map is drawn with MapLibre GL JS and PMTiles, and the site is built with Astro. These are open-source projects under their own licences.

Using our images and embeds

Images you download from the map and the embed code both carry the credits above. Please leave them in place.

Open database licence notice (ODbL) for the empire extents

Province and empire extents: Ancient World Mapping Center (UNC-Chapel Hill), derived from the Barrington Atlas of the Greek and Roman World and OpenStreetMap, ODbL 1.0.

The empire outlines and province areas on this site are an adapted database made from the AWMC geodata (the AD 117 and AD 200 outlines, and the AD 200 province lines turned into areas). We therefore publish them under the same licence, the Open Database Licence (ODbL) 1.0. You may copy, share and adapt them, including commercially, as long as you credit AWMC and OpenStreetMap as above, say that your version is derived from this one if you change it, and share your changed version under the ODbL too.

• extents.geojson: the 13 key-date outlines, one feature per date and part (whole, east, west), with area and a note on how each was built.
• provinces.geojson: the 43 province areas of AD 200, with names, capitals, dates and a flag for merged units.

Each file carries the licence and attribution inside it. Pictures you download from the map carry the credit line, and the embed code does too, so please leave them in place.

How the dates are built

AWMC publishes outlines for 60 BC, AD 117 and AD 200 only. AD 117 and AD 211 use AWMC's AD 117 and AD 200 outlines directly. The other provincial dates (133 BC, 44 BC, AD 14, 395, 476 and 565) join the AD 200 province areas that were Roman at the date, using the table below, and clip the Republican dates to AWMC's 60 BC outline. 264 BC and the Byzantine dates of AD 1000, 1180 and 1453 use modern regions from Natural Earth chosen by a committed list. The outline for 753 BC is a symbolic 1.5 km circle around Rome.

This means early frontiers take their shape from the AD 200 provinces, and some AWMC units combine several provinces. The extent notes in extents.geojson say so for each date.

Cited tables of dates

The dates when each province was annexed and lost, and the key-date events, are historical facts collected in two small tables in our pipeline, each row with a source note. They are summarised here.

Key dates

Provinces

How the numbers are worked out

EPSG:6933 (WGS 84 / NSIDC EASE-Grid 2.0 Global), on the extent before simplification. A modern country counts as inside the empire at a date only if at least 500 km² of it is inside, because the ancient and modern coastlines do not match exactly. Shares are measured against the part of each country inside a box around the Mediterranean world, so that overseas territories do not count. Areas are land inside the extent, measured in the equal-area projection EPSG:6933. Published estimates of the empire's size vary with how the frontiers are drawn and with whether client states and seas are counted.

Country pages are indexed only when the country had enough inside the empire and enough Roman-period places: page when (max share >= min_share or max area >= min_km2) and the country has at least min_cities Roman-period Pleiades settlements.

Not used

We did not use the historical-basemaps collection of world borders, because its data licence is not stated.