This study quantifies the importance of the Roman military for the development of a market economy in north-western Europe. Distributions of low denomination coins show how the Roman arrival kick-started a local market economy. Additionally settlement densities of fluvial catchments are used as a proxy for economic development. Our newly constructed dataset of settlement sizes shows a high correlation with Roman military requirements. After the demise of the empire the local market economy faded away. This antique market economy had a different geographical distribution than its medieval successor, which was not mainly driven by military demand.