Nuremberg is often referred to as having been the 'unofficial capital' of the Holy Roman Empire, particularly because Imperial Diet (Reichstag) and courts met at Nuremberg Castle. The Diets of Nuremberg were an important part of the administrative structure of the empire. The increasing demand of the royal court and the increasing importance of the city attracted increased trade and commerce to Nuremberg. In 1219, Frederick II granted the “Großen Freiheitsbrief” (Great Letter of Freedom), including town rights, Imperial immediacy (Reichsfreiheit), the privilege to mint coins, and an independent customs policy, almost wholly removing the city from the purview of the burgraves. Nuremberg soon became, with Augsburg, one of the two great trade centers on the route from Italy to Northern Europe.