In 1569 the very powerful Merchant's Consulate of Seville commissioned Tomas de Mercado (its moral adviser) to write the Suma de tratos y contratos. It was a widely read book and had a great influence in the commercial world of the epoch. The interest in the mercantile practice and its real and technical manifestations led Tomas de Mercado to be interested in the places and situations in which this practice became more intense and articulated. This explains the very high frequency with which Mercado refers to fairs in his treatise. They are mentioned in almost all the chapters of the Suma de tratos y contratos, which clearly shows that the activities related to fairs touched practically all areas of the life of the merchants of the epoch.