To determine ancient shipping routes and travel times, a specialized navigation software program was used to simulate ancient voyages. Originally aimed solely at allowing a better understanding of the business model of a Roman trader in the first century ad by making a reliable estimate of the travel time on the main trading routes, this new method makes a contribution to a number of related debates, such as providing new aspects on the actual routes taken, the sailing capabilities of Roman merchantmen and the explanation of the shipping rates in Diocletian’s Edict on Maximum Prices. The computer permits simulating the complex interaction of a Roman sailing boat with the dynamic weather systems it encountered on its route and calculates the route under real weather conditions by virtually simulating a journey. The results obtained through this formal modelling and computational simulation, and further work on the technical sophistication of the model by adding more performance data from reconstructed ships and more ship types, such as warships, allow us to address a wider range of research questions, even beyond the Roman economy. Shipping shaped antiquity. The better we understand shipping, the better we understand antiquity. The method presented in this paper contributes to that goal.