The Architecture of Istanbul describes a large mixture of structures which reflect the many influences that have made an indelible mark in all districts of the city. The ancient part of the city (the historic peninsula) is still partially surrounded by the Walls of Constantinople, erected in 5th century by the Emperor Theodosius II to protect the city from invasion. The architecture inside the city proper contains buildings, statues, and functional constructions which came from Byzantine, Genoese, Ottoman, and modern Turkish sources. The city has many architecturally significant entities. Throughout its long history, Istanbul has acquired a reputation for being a cultural and ethnic melting pot. As a result, there are many historical mosques, churches, synagogues, palaces, castles and towers to visit in the city.