The Golden Gate of Vladimir, constructed between 1158 and 1164, is the only preserved ancient Russian city gate. A museum inside focuses on the history of the Mongol invasion of Russia in the 13th century.
The Golden Gates existed in the holiest cities of Eastern Orthodoxy: Jerusalem, Constantinople, and Kiev. On making Vladimir his capital, Andrew the Pious aspired to emulate these structures, commissioning a lofty tower over the city's main gate to be erected in limestone and lined with golden plaques. According to ancient Russian chronicles, the masons were invited from Friedrich Barbarossa. The main arch used to stand 15 meters tall. The structure was topped with a barbican church dedicated to the Deposition of the Virgin's Robe and symbolizing the Theotokos's protection of Andrew's capital.
The gate survived the Mongol destruction of Vladimir in 1237. By the late 18th century, however, the structure had so deteriorated that Catherine the Great was afraid to pass through the arch for fear of its tumbling down. In 1779, she ordered detailed measurements and drawings of the monument to be executed. In 1795, after many discussions, the vaults and barbican church were demolished. Two flanking round towers were constructed in order to reinforce the structure, and artisans then reconstructed the barbican, following the drawings made in 1779.
References:The Walls of Constantinople are a series of defensive stone walls that have surrounded and protected the city of Constantinople (today Istanbul) since its founding as the new capital of the Roman Empire by Constantine the Great. With numerous additions and modifications during their history, they were the last great fortification system of antiquity, and one of the most complex and elaborate systems ever built. They were also the largest and strongest fortification in both the ancient and medieval world.
Initially built by Constantine the Great, the walls surrounded the new city on all sides, protecting it against attack from both sea and land. As the city grew, the famous double line of the Theodosian Walls was built in the 5th century. Although the other sections of the walls were less elaborate, they were, when well-manned, almost impregnable for any medieval besieger.