External enemies and the complex internal crisis caused by Iconoclasm affected the economic life of the Macedonian region. Avar and Slav incursions in the 6th and 7th centuries, as well as the earthquakes that struck in the second decade of the 7th century, destroyed many towns and cities (e.g. Philippi and Thasos).
Miniature from the Chronicle of Ioannis Skylitzis,
Because of the new conditions prevailing, the populations of many of these cities were transferred to naturally defensive positions that were subsequently fortified with walls (Beroia, Edessa, Servia, Stoboi, Vargala, Kaisareia (ancient Aiane), Amphipolis, Serrhai, Stromnitsa). At the same time, country dwellers took refuge in mountainous regions and in caves in which they folded their flocks.
The gradual absorption of the Slavs, however, and the growth of their commercial relations with the local Greeks aided the development of towns and cities. Thessalonike in particular was prominent in the economic and commercial activities of the region throughout this period, a fact reflected in the existence of various public officials, such as the 'kommerkarios', who regulated economic life and controlled shipping and its movements. Even during siege periods, vessels sailed into its harbour with timber, cereals, and pulses for the great state warehouses of the city.
The second most important Macedonian port was Christoupolis (present-day Kavala), also the seat of a 'kommerkiarios' who levied a 10% tax on all goods moving through the port.