The "Book of the Eparch", which dates to the 10th century, gives a detailed picture of the city's commercial life and its organization at that time. The corporations in which the tradesmen of Constantinople were organised were supervised by the Eparch, who regulated such matters as production, prices, import, and export. Each guild had its own monopoly, and tradesmen might not belong to more than one. It is an impressive testament to the strength of tradition how little these arrangements had changed since the office, then known by the Latin version of its title, had been set up in 330 to mirror the urban prefecture of Rome.