In the Itiner-e atlas a main road is a well-attested Roman route, backed by at least two of milestones, an ancient itinerary and a known major road. Every other road is secondary. On our map main roads are drawn with the thicker line.
Key takeaways
- A segment counts as a main road if it has more than one of three signs: milestones, a place in an ancient itinerary, or a shared course with a known major road.
- Main roads are 34.6% of the network (103,478 km) and secondary roads are 65.4% (195,693 km).
- The labels come mostly from earlier published studies, and Itiner-e applies its three-sign rule only where those are missing.
- Main or secondary says how well documented a road is, not who built it or how wide it was.
How the main and secondary split works
Itiner-e gives each road segment a type: "Main Road" or "Secondary Road". It is a simple two-tier hierarchy rather than a ranking of every road [1].
For most segments the label simply follows earlier archaeological and historical publications that the atlas digitised. Where those do not say, the team applied a rule. A segment is a main road if it has more than one of these three characteristics [1]:
1. There are milestones on it. 2. It is part of an ancient itinerary, chiefly the Antonine Itinerary or the Tabula Peutingeriana. 3. It shares much of its course with a major road known from nineteenth or early twentieth century maps.
Everything that does not pass is secondary. The authors describe main roads as the core of the Roman land transport network, the ones best documented through milestones or historical sources, and say the total is unlikely to grow much because these are the most studied roads. Secondary roads, by contrast, show more local movement, and more of them may be found as understudied areas are surveyed [1].
On the map, main roads are the thicker lines and secondary roads the thinner ones. The legend sits in how to read the map.
An example from our data
Our map holds 5,698 main-road segments and 9,071 secondary segments. By length, main roads add up to 103,478 km, which is 34.6% of the 299,171 km total, and secondary roads to 195,693 km, or 65.4%.
Secondary roads therefore make up the larger share of the network, even though main roads are the better known. The named roads are a good place to see the thick lines: open Watling Street, which is 352 km long in 58 segments, or the Via Egnatia, the longest named road at 1,165 km. For a country-level picture, try the United Kingdom page.
The thing people get wrong
It is easy to assume that "main" means "wider", "better built" or "built by the state". The atlas does not say that. Its test is about documentation: milestones, itineraries and a known later reputation [1]. A road could be very important in its day but be missing from the sources, and so be classed as secondary. In the other direction, a main-road label does not mean we know its line any better. A main road can be conjectured, and many are: see road certainty.
Frequently asked questions
Is a secondary road a minor track?
Not necessarily. It is a road that does not meet the atlas test for a main road. Many are local roads, and some may have been busy ones that are simply less documented.
How much of the network is main road?
34.6% of the length, or 103,478 km in 5,698 segments.
Does the line thickness say anything about certainty?
No. Thickness shows type, and the solid, dashed or dotted pattern shows certainty. Any combination can occur.
Sources
- Itiner-e: A high-resolution dataset of roads of the Roman Empire, Scientific Data (Brughmans et al., 2025).
- Itiner-e: the digital atlas of ancient roads, Itiner-e.
- Every figure from our own map is worked out from the datasets on the data sources page (checked against Itiner-e version 2024 1.3).