It has long been recognised that Pompeii preserves important clues to the functioning of a traffic system. Particularly suggestive are the ruts worn in the surface of the street paving, but these are combined with bollards and blocking stones to indicate that certain streets were inaccessible or accessible only from one direction. The evidence of the ruts was first systematically collected by Sumiyo Tsujimura over twenty-five years ago (Reference Tsujimura1991), but her approach consisted chiefly in plotting the comparative depth and form (straight or curved) of the ruts. The new study under review takes Tsujimura’s work forward and analyses the material with a whole new rigour and subtlety.

Poehler’s main contribution is to bring the vertical surfaces of the street into play; he argues that the wearing created by cart wheels where they overrode or rubbed against features such as stepping stones, kerbstones and guard stones can in most cases be used to establish the direction of traffic flow. At the same time, it is clear that directions valid for one period were not necessarily (to use an unfortunate metaphor) set in stone: they could be the subject of revision. Similarly, there are signs that not all drivers abided by the rules. Nevertheless, certain generalisations can be made; notably, that streets wide enough to accommodate two lanes of traffic were two-way streets, and that Pompeians normally drove on the right (though wherever possible hogging the middle of the road). Of course, the nature of the evidence means that Poehler’s conclusions – especially where they are dependent on touch rather than visual observation – have to be taken on trust; but his arguments are so detailed and circumstantial that they carry conviction. He is even able to establish traffic detours introduced to ease congestion at some of the main junctions in the city.

Having established the rules of the road, the author applies a broader brush. An imaginative re-evocation of a muleteer’s journey through Pompeii gives an immediacy to life on the streets besides enabling us to venture some conjectures as to how the city took decisions on traffic flow and how the relevant information was disseminated to the drivers who put the system into practice. A following chapter collects evidence for traffic data from twenty-four other sites in the Roman world (and confirms how lucky we are to have the data from Pompeii). Finally, the author attempts to write a brief history of traffic management from early Republican Italy to the High Empire. This section shows a mastery of the source material, including the legal codes; indeed, the whole book is a remarkable achievement. Original, painstaking and written in a lively style, it represents scholarship of the highest order – and opens new insights into an important aspect of the functioning of ancient cities.