In the present study, humeral and femoral midshaft circumferences were used in the weight estimation of dogs from the ancient site of the Theodosius Harbor in Istanbul. According to the calculations taken on each humerus and femur, body weight distribution of the Byzantine dogs from the Theodosius harbour was observed to be 7.953-22.385 kg. The relative ease to accommodate Terrier-size dogs in urban environments may have led to a preference for such breeds in Constantinople. It is possible that these 'light-and medium-sized mesocephalic dogs' were also used as 'alarm' guards in Constantinople. We suggest that the presence of several bones in the Yenikapi excavation area may indicate that dogs were simply buried or dumped as rubbish after death in everyday life in Constantinople.