The central thesis of this paper is that the Romans used land surveys and maps as integral parts of the road design process. This is not the conventional view, and is in direct contradiction to a fundamental assumption made by the acknowledged master of the subject, I.D. Margary. After praising the achievements of the Roman road builders he writes: ‘…it should be remembered that no maps or compasses were available to them.…’ As far as the magnetic compass is concerned, it certainly seems unlikely that it was familiar to the Romans, but the sun-dial offered a reliable, if less convenient, alternative method of finding the north–south direction. However, the supposed absence of maps is more critical, and has led to the putting forward of many exotic theories to explain how the roads were designed and laid out. Despite their ingenuity, these theories are highly impractical, yet still fail to explain how the Roman engineers solved the problems they faced. This paper shows that available knowledge and equipment were quite adequate to allow the Romans to design their roads with the same level of careful planning as they demonstrated in other fields of technical endeavour.