The Walls of Constantinople were a series of defensive fortifications built to protect the city of Constantinople, the capital of the Byzantine Empire. Constructed primarily in the 4th century and later expanded, these walls included a double line of walls with towers and a moat, making them one of the most formidable defenses of their time. The walls successfully defended the city against numerous attacks for centuries, including the famous siege by the Ottoman Empire in 1453. Despite their strength, the walls were eventually breached, leading to the fall of Constantinople and marking the end of the Byzantine Empire.