The town's growth was disrupted in 1770, because of conflict that erupted between Kozani's local inhabitants and Kozanite merchants in central Europe, who contributed to the town's prosperity; even more catastrophically, the city was pillaged by Turkish beys in 1770. A subsequent incursion by Aslan bey, in 1830, ravaged the city immensely. In 1855 next to St. Nicholas Church a 26 meters high bell tower was built, which would become the symbol of the city. In 1939, a clock was added to the top of the tower, donated by Greek-American, Konstantinos Mamatsios. According to the 1904 population census, 12,000 Greeks and 350 Aromanians (Vlachs) were living in Kozani at the time.