When compared with modern travel across Europe, North Africa, and the Middle East, journeys in Roman times were more likely to be measured in days or weeks rather than hours. Today, the average flight from London to Rome takes between 2.5 and three hours, whereas this journey could have taken between three and six weeks in Roman times, depending on the cost and mode of transport. When looking at journeys from Rome to other major cities outside the Italian peninsula, those that utilized travel across the Mediterranean were generally the fastest in relation to total distance. For example, the cheapest journeys to Lugdunum and Carthago were of similar distance, but the land journey to Lugdunum was roughly three or four times as long as the sea journey to Carthago (depending on the season), and this was also true for military movements.
Infrastructure
The Romans were notably famous for their road networks, with eventual totals of over 400,000 kilometers of road; 20 percent of which was paved. This infrastructure was essential to the defense of the empire, as it allowed much greater movement for Rome’s armies, as well as economic sustainability, for the movement of merchants, slaves, and cargo. Sea trade and transport was also an essential part of the Roman Empire's success, however Rome controlled virtually all of the Mediterranean coast by 200CE, therefore there was no major military threat at sea apart from pirates.
Methodology
These figures come from ORBIS: The Stanford Geospatial Network Model of the Roman World, which was launched in 2013 by a team of historians and IT specialists at Stanford University. It is an attempt to give greater insight into the logistics of travel through the Roman Empire, in conditions similar to those of 200CE (although some locations did not exist at this time). Users can create hypothetical, approximate journeys across the empire, looking at the duration, distance, and price per journey. The model takes various factors into account, including seasonal variations (such as the weather’s impact on sea travel or mountainous journeys), modality of transport, and pricing variations, among many others. While the source acknowledges it uses a simplified model of the transport network across the empire, there are over 363,000 possible outcomes for journeys between 632 sites, making this the most comprehensive model of its kind.