The noun mercatus (plural mercatūs) means "commerce" or "the market" generally, but it also refers to fairs or markets held immediately after certain ludi. Cicero said that Numa Pompilius, the semi-legendary second king of Rome, established mercatus in conjunction with religious festivals to facilitate trade, since people had already gathered in great numbers. In early times, these mercatus may have played a role in wholesale trade, but as commerce in Rome became more sophisticated, by the late Republic they seem to have become retail fairs specialized for the holiday market. The Sigillaria attached to the Saturnalia may have been a mercatus in this sense. Surviving fasti record Mercatus Apollinares, July 14–19; Mercatus Romani, September 20–23; and Mercatus Plebeii, November 18–20. Others may have existed. The English word "fair" derives from Latin feria.
Read more about this topic: Roman Festivals