Aetolia in the Byzantine and post-Byzantine times is little known from any historical evidence, although due to its key position, close to important sea routes, it was an significant, albeit provincial, part of the Empire. The long period that followed Antiquity was characterised by constantly changing historical conditions, natural disasters, such as the great earthquake of the mid-6th century AD, insecurity, invasions and military conflicts. Despite the multitude of monuments it contains, little is known about the local craftsmen or its ecclesiastical and spiritual life, and indeed no monastery libraries have survived. Nevertheless, inscriptions indicate the presence of scribes writing books, educated clergymen and monks.
During the Early Byzantine period, Aetolia belonged to the Metropolis of Old Epirus, with its seat at Nikopolis. Christianity began to spread from the beginning of the 4th century AD into western mainland Greece, with the Diocese of Nafpaktos as its main base. In the Early and Middle Byzantine period, the formerly established settlement nuclei remained the centres of population concentration. More specifically, in the wider area of Messolonghi during the Early Byzantine period, Christian basilicas were founded near or on top of older settlements (Kryoneri, Agios Georgios or those in the area of Pleuron). These buildings were abandoned by the 10th century and their sites were often used as cemeteries.
In 896-900 the metropolis and the seat of Epirus was transferred to Nafpaktos. In south-western Aitoloakarnania lies the Diocese of Acheloos, the seat of which is placed by many scholars in the Episcopal of Mastrou (St. John the Baptist) or in the Dio Eklissies in Stamna. Yet other locations have been proposed.
There are many monuments, mainly of the Byzantine period around Messolonghi, which show a significant preference for being positioned on the perimeter of the lagoon. Most of them have undergone many building phases, while some are now in ruins. Churches of the basilica type, such as the church of Agios Georgios in Evinochori, continue to be used in this period. Occasionally they were built on top of older buildings, incorporating ancient material in their construction, while at the same time the use of wood, abundant mortar and limited brickwork was common.
Alongside the predominantly ecclesiastical buildings and the church-building activity that developed, the use of caves as monastic centres or ascetic retreats began in these years. An organised monastic movement spread, which included the complexes on the mountains of Varassova and Zygos.
From the 13th century, the area became part of the Despotate of Epirus and the development of arts and crafts and a tendency to decorate the exteriors of the churches with moulded ceramic elements is to be noted. In the mid-14th century, after constant fighting between various rulers, the region was occupied by Albanians.
This was followed by the Turkish conquest in the mid-15th century. During the centuries of Turkish rule, the region of Aetolia lived through the conflicts of the Venetian-Turkish wars, the pirate raids on the coasts and the constant movements of populations in search of safety, right up until the outbreak of the Greek Revolution. During the same period, the church architecture shows a variety of architectural forms, while the koulies-watchtowers came to represent the typical fortified dwelling, providing protection from raids, so common in this insecure era.
