Historiansof the Roman economy appear to agree that during the period 200 BC—AD 200 the Gross Domestic Product of the overall empire grew, however moderately.

They explain this phenomenon partly as the result of a reduction in transportation costs and in ‘transaction costs’ - that is, the sum of the costs of looking for oppor­tunities for exchanging goods and services, reaching agreements between parties through contracts, and enforcing transactions.¹ This reduction is said to be due, among other causes, to the development of a common legal system, ‘especially in the field of commercial law’.² This statement raises the following questions: What is ‘Roman commercial law’? Where does it come from? How did it develop? And how does it fit in the wider field of Roman law? This chapter will attempt to provide some answers.

1.