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 12th 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 Theophilos (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).