Fired bricks, one of the oldest man-made building materials, are historical documents that reflect the production technologies of their periods and the raw material characteristics of the geography they were located. Characterization of bricks is essential for revealing production techniques of their times and contributing to conservation works on monuments built with this material to pass through next generations. The fired bricks were frequently used as one of the important building materials in Byzantine Architecture. In this study, the fired bricks collected from the different construction periods of St. Jean Basilica, Ayasuluk Hill and Anaia Church, Kadıkalesi, which belong to the Byzantine Period, were investigated to determine material properties, periodical differences, and production technologies. The properties of Byzantine bricks were determined by standard test methods, compression tests, SEM-EDS, XRD, FTIR, and TGA analyses. According to the results, brick samples taken from both areas were highly porous and low-dense materials. Ca-poor clay source was used in producing St. Jean Basilica bricks, while Anaia Church bricks were produced with Ca-rich clay sources. This situation was decisive in the colour of bricks, and St. Jean Basilica bricks were in reddish colours, while Anaia Church bricks were in brown/beige colours. Also, raw material was extracted from a single source in the production of all St. Jean Basilica bricks, while two different sources were utilized for Anaia Church bricks throughout the three construction periods. Besides, the bricks of both churches were found to be fired at low temperatures (700–900°C) due to the technology of Byzantine kilns. Despite low firing temperatures, the majority of the bricks did not possess pozzolanic properties since they did not contain a sufficient amount of clay minerals. The highest mechanical strength was determined in the bricks with higher firing temperature and bricks with the higher calcium content. The properties of fired bricks were differentiated based on production technologies; contrary, a distinctive difference was not observed depending on their periods.