Complex topic - Byzantine commerce and coinage, mainly at the very height of the empire. 10th - 12th century.

Byzantine commerce, which was essentially based on trading of different materials, was the main lifeline of the Byzantine economy. For hundreds of years, up until around the 14th century, the Byzantine Empire relied on this vital trade to boost the coffers, ensure a stable army and to ensure the vast development of the empire. Despite it being a rather agricultural economy, trade was crucial for the Byzantines as it would have been impossible without this valuable commerce to exist and flourish. Traded goods were usually silk, grains, wines, meat, fish and other items that were sent in all corners of the planet. (Silk worms were smuggled from the Far East, for example)

Over time, trade declined - but that's due to a number of different reasons.

How come the Italian Republics managed to outmaneouver the Byzantine merchants and secure the trading for themselves? After the reign of Basil the IInd, the empire's importance in global (at least European) trade declined, replaced by the Republics. Why? How come the Republics' merchants secured the trade for themselves?

And second - how come the Byzantine coinage, particularly the ones before the hyperpyra of Alexios I, become the main (at least the most important) coin of the Mediterranean world? Simply because of the Byzantine Empire's prestige?