What was one of the greatest tactical advantages the Byzantine military had over its foes

Well the Byzantines' capital of Constantinople was almost completely surrounded by water. This gave them the advantage in anyone tried to invade them. They also built a large wall all around the city with protected the people from outsiders. They also invented Greek fire, which was fire that could not be put out by water. This was extremely useful to attack ships. They also put large chains in the water to prevent ship from getting through.