Systems & Society · Civilization Systems Lab
The Roads to Rome
Imperivm Romanvm · c. 200 CE
A ruler, a merchant, or a legion never experienced the empire in kilometers — they experienced it in days and denarii. This lesson runs a live shortest-path planner across a simplified network of the Roman world, modeled on ORBIS, an open-source geospatial project built by historians and engineers at Stanford University. Pick a city below and watch the network find your road to Rome.
Big Question
How do you measure an empire — not in miles, but in time and cost?
Distance on a map is fixed. Distance in the real world depends on the road you're on, which way the wind blows, and what season it is.
What Is ORBIS?
An Empire, Turned Into a Network
ORBIS treats the Roman world the way a computer scientist treats a subway map: as a network of nodes (cities, ports, mountain passes) connected by edges (roads, rivers, sea lanes), each weighted by how long it takes to cross and how much it costs. Ask it for a route and it calculates the fastest, cheapest, or shortest path across the empire — accounting for season, direction, and mode of transport. That's exactly the kind of weighted shortest-path problem this page solves live, in miniature, below.
751
settlements, ports, and mountain passes modeled as network nodes
268
of those sites are seaports, linked by nearly 1,000 sea routes
50,000 mi
of Roman roads and desert tracks included in the model
20,000 mi
of navigable rivers and canals connecting inland cities to the sea
Figures from the ORBIS v1.0 project paper, Scheidel & Meeks (2012), Stanford University. Explore the full live tool at orbis.stanford.edu.
Live Route Planner
Find Your Road to Rome
This is a simplified teaching model with 10 sample cities and 15 illustrative routes — not the full 751-node ORBIS dataset. Distances, days, and prices are approximate and built to illustrate the same forces ORBIS models in full detail: mode, season, and cost. For real computed figures, use the live tool linked above.
Four Ways to Travel
The Modes ORBIS Models
Every edge in the network above belongs to one of these modes, and each moves people and goods at a different price and a different speed.
Wagons, pack animals, marching soldiers. Reliable, but slow — and by far the most expensive way to move heavy cargo.
Barges on navigable rivers and canals. Cheaper and faster than road, especially heading downstream.
Ships hugging the shoreline, able to put in at port if weather turned. Slower than open sea but safer.
Ships crossing open water on favorable winds — the fastest, cheapest mode, but the riskiest, and closed in winter.
The Sailing Season
Mare Clausum — The Closed Sea
Roman sailors avoided the open Mediterranean in winter. The military writer Vegetius records the sailing season running roughly from March 10 to November 11; outside that window, storms made open-sea crossings dangerous enough that most captains simply waited. Flip the planner above to Winter and watch the direct open-sea routes fade out on the map — journeys that took days in summer can take weeks once ships are forced onto slower coastal and overland detours.
Cost Lab
Why Ship It, Not Cart It?
Rome's Edict on Maximum Prices (301 CE) fixed shipping rates across the empire — and the numbers reveal just how lopsided ancient transport costs were. Moving cargo by sea cost only about one-fifth as much per mile as hauling the same cargo overland by wagon. Try the slider: for a shipment moving the same distance, see how the cost changes by mode.
Why It Mattered
Because land transport was so expensive, a coastal city could import grain from across the Mediterranean more cheaply than cart it in from farmland a few days' wagon ride away. Rome itself depended on grain fleets from Egypt and North Africa rather than the farms of Italy's interior.
River ratio is illustrative, between road and sea. Based on Scheidel, "Explaining the Maritime Freight Charges in Diocletian's Prices Edict," Journal of Roman Archaeology.
Field Work
Run the Real Model
The planner above is a simplified teaching model. The real ORBIS tool computes actual routes from real historical data. Open orbis.stanford.edu, pick Roma as your destination, and fill in this table for three cities of your choice — try Alexandria, Carthago, and Constantinopolis (Byzantium) to start.
| Starting city | Fastest route, July (days) | Fastest route, January (days) | Cheapest route, July (days) |
|---|---|---|---|
Then compare: how close did the real ORBIS numbers come to what our simplified planner predicted above? Which mattered more for your routes — season or mode?
Think
Discussion Prompts
Open Source Credits
Built on Public, Open-Source Research
ORBIS was created by Walter Scheidel (historian) and Elijah Meeks (digital humanities engineer) at Stanford University Libraries, first released in 2012. Its underlying database and code are published on GitHub under the MIT License — meaning anyone, including a classroom, can read it, learn from it, and build on it. That is exactly what this lesson does: it takes the same ideas ORBIS models in full detail and turns them into a hands-on teaching tool.
The coastlines, rivers, and city positions on the map above are drawn from real geographic data — Natural Earth, a free, public-domain map dataset — rather than hand-sketched shapes, projected to fit the extent of the Roman world.