<P> Ever since the creation of the Byzantine monetary system by Constantine in 312, its pivot had been golden solidus, a coinage whose nominal value was equal to its intrinsic value, as is proven by the Theodosian Code . Solidus became a highly priced and stable means of storing and transferring values Novel 16 of Valentinian III punished with death anyone who dared "refuse or reduce a gold solidus of good weight ." Weight and fineness of the coinage were joined by another element: the authenticity of the stamp, which served to guarantee the other two . Alongside this "real" - value gold coinage, and a slightly overvalued silver coinage, there was also a bronze coinage of a fiduciary nature that made up the second specific feature of the monetary system . At the end of the 10th and in the 11th centuries, money underwent a profound transformation, followed by a crisis; the denomination affected all metals at different dates, and according to different modalities . The reform of Alexios I Komnenos put an end to this crisis by restoring a gold coinage of high fineness, the hyperpyron, and by creating a new system destined to endure for about two centuries . </P> <P> In 1304 the introduction of the basilikon, a pure silver coinage modeled on the Venetian ducat marked the abandonment of Komnenian structures under the influence of western models . The system that began in 1367 was constructed around the stavraton, a heavy silver, equivalent to twice the weight of fine metal of the last hyperpyra . By the end of the 12th century, especially from 1204 on, the political fragmentation of the empire resulted in the creation of coinages that were either "national" (e.g. in Trebizond in 1222, in Bulgaria in 1218, and in Serbia in 1228), colonial or feudal . Venetian coins soon penetrated the monetary circulation in Byzantium . This situation stands in contrast with the monopoly that Byzantine currency had enjoyed until the 12th century, within its own frontiers, and through its diffusion in the lands beyond--a measure of its political and economic influence . </P> <P> One of the economic foundations of the empire was trade . Constantinople was located on important east - west and north - south trade routes . Trebizond was an important port in the eastern trade . The exact routes varied over the years with wars and the political situation . Imports and exports were uniformly taxed at ten percent . </P> <P> Grain and silk were two of the most important commodities for the empire . The Arab invasion of Egypt and Syria harmed the Byzantium's trade, and affected the provisioning of the capital with grain . As the population increased in the 9th and 10th centuries, the demand for grain also increased . There was a functioning market for grain in Constantinople, but it was not entirely self - regulating: the state could play a role in the availability of grain, and the formation of prices . </P>

How did constantinople serve as a center of trade