The main coin used was the Hyperpyron, a trachy shaped coin that weighed in theory 4.45gm . The size was around 30mm The coin was minted in two locations, Constantinople, the empires capital and in Thessalonica. The difference between the mints was the style used. The coins minted in Constantinople were thinner and Thessalonica they were thicker, visually the same but in hand the difference becomes apparent. The coin was not used in everyday transactions, that is why the are normally found in nice condition. The way the system worked was simplistic, Taxes were paid in gold. The common citizen was not paid in gold but in the lesser denominations of Billion trachea, Billion tetartera and AE tetartera. So pay tax they had to take their lesser denominations and bring them to the money changer, he for a profit would change the coin into gold coinage. So if their was change due for the tax, the state would pay in tetartera or billion trachea ( It depends on location) As of a result, coin collectors have the ability to collect beautiful coins in gold with minor circulation. The other denominations that were used for everyday transactions remained in circulation, never to be recalled and rarely found in an attractive state. Here are 4 Hyperpyron, 2 from Alexius 2 from his son John II. The other form of gold during the time was the trikephalon, known today in the collecting world as the EL aspron trachy. It took 3 of these to equal a hyperpyron. It was a mixed metal coin made of gold, sliver and copper. This coin and the other mixed metal coins were criticized during the time. The reason it was virtually impossible to determine what percentage of the metals were used. This coin circulated in Asia minor with billion trachea, whereas the Hyperpyron circulated in the city and in the western part of the empire. We have no idea why the denominations were kept separate, same is true for the billion trachea and tetartera, they only comingled in the capital, the rest of the empire they were kept separate. This is determined by hoard finds and recorded single loss coinage. Here are Trikephalon from John II Here are Trikephalon from his famous son, Manuel I Comnenus The coin reform stayed intact until the mid 14th century, the most notable change was the debasement of the gold coins. The need for coinage at the time was considerable, huge amounts of coins were minted making this an excellent time period for collectors to specialize in. It also leaves gold coinage in a much more affordable range for the average collector. Show off your Byzantine gold, from this time period or earlier.