Until the eleventh to twelfth century Byzantium commanded a particularly advanced war technology, compared to the standards of the medieval world. This article presents relevant evidences concerning fortification and siege technology and refers to the so-called Greek fire, to certain portable weapons, to the equipment of warriors and to the harness of their horses as well as to war ships. The capture of Constantinople by the crusaders in 1204 deprived the Byzantines of the distinguished position they had hold in war technology.