Further evidence is provided by the coinage of the empire in this period. After a long period in the early middle ages during which the only coins were struck in Constantinople, the twelfth century saw the return of a provincial mint regularly operating at Thessaloniki. Yet the most convincing evidence for what Harvey calls a "substantial increase in the volume of money in circulation" comes from the quantity of coins found on archaeological sites. Thousands of coins have been found both at Athens and at Corinth. Some idea of the scale of the expansion that took place here can be gained from comparing the number of Corinthian coins dating from the reign of Theophilus (813-842), at the start of the expansion, with the number of coins dating from other periods. Harvey states that "About 150 coins can be attributed to this emperor compared with only twenty from the previous century". By contrast, excavations in 1939 revealed 4495 coins dating from the reign of Alexios I Komnenos (1081-1118) and 4106 coins from that of Manuel I Komnenos (1143-1180). At Athens, coins from the Komnenian period have also been found in abundance (over 4,000 from Manuel's reign).
Similar evidence of economic expansion has been discovered elsewhere in the empire, especially in the European provinces. In Asia Minor, some areas had become depopulated due to Turkish raiding in the late eleventh century. Yet as the Komnenian emperors built up extensive fortifications in rural areas during the twelfth century, repopulation of the countryside took place. The restoration of order in western Asia Minor enabled the demographic trend to resume its upward course after the setbacks of the late eleventh century, and indeed it was in the thirteenth century that this process reached its peak. It is quite possible that an increase in trade, made possible by the growth of the Italian city-states, may have been a factor in the growth of the economy. Certainly, the Venetians and others were active traders in the ports of the Holy Land, and they made a living out of shipping goods between the Crusader Kingdoms of Outremer and the West while also trading extensively with Byzantium and Egypt.
Overall, given that both population and prosperity increased substantially in this period, economic recovery in Byzantium appears to have been strengthening the economic basis of the state. This helps to explain how the Komnenian emperors, Manuel Komnenos in particular, were able to project their power and influence so widely at this time. Yet this is by no means the only effect of economic expansion in the empire; the effect on Byzantine Culture and society was also quite profound, as we shall see.
The new wealth being generated during this period had a positive impact on Byzantine cultural life. In artistic terms, the twelfth century was a very productive period in Byzantine history. There was a revival in the mosaic art, for example, with artists showing great interest in depicting natural landscapes with wild animals and scenes from the hunt. Mosaics became more realistic and vivid, with an increased emphasis on depicting three-dimensional forms. In the provinces, regional schools of Architecture began producing many distinctive styles that drew on a range of cultural influences. All this suggests that there was an increased demand for art, with more people having access to the necessary wealth to commission and pay for such work. According to N.H.Baynes in Byzantium, An Introduction to East Roman Civilization,
"With its love of luxury and passion for colour, the art of this age delighted in the production of masterpieces that spread the fame of Byzantium throughout the whole of the Christian world. Beautiful silks from the work-shops of Constantinople also portrayed in dazzling color animals -lions, elephants, eagles, and griffins- confronting each other, or representing Emperors gorgeously arrayed on horseback or engaged in the chase."
"Yet the marvellous expansion of Byzantine art during this period, one of the most remarkable facts in the history of the empire, did not stop there. From the tenth to the twelfth century Byzantium was the main source of inspiration for the West. By their style, arrangement, and iconography the mosaics of St. Mark's at Venice and of the Cathedral of Santa Maria Assunta at Torcello clearly reveal their Byzantine origin. Similarly those of the Palatine Chapel, the Martorana at Palermo, and the cathedral of Cefalù, together with the vast decoration of the cathedral at Monreale, demonstrate the influence of Byzantium on the Norman Court of Sicily in the twelfth century. Hispano-Moorish art was unquestionably derived from the Byzantine. Romanesque art owes much to the East, from which it borrowed not only its decorative forms but the plan of some of its buildings, as is proved, for instance, by the domed churches of south-western France. Princes of Kiev, Venetian doges, abbots of Monte Cassino, merchants of Amalfi, and the Norman kings of Sicily all looked to Byzantium for artists or works of art. Such was the influence of Byzantine art in the twelfth century, that Russia, Venice, southern Italy and Sicily all virtually became provincial centres dedicated to its production."