The Moscow Kremlin (Russian Московский Кремль; wiss. Transliteration Moskovskij Kremlʹ) is the oldest part of the Russian capital Moscow and its historical center. The original castle on the Moskva River, dating from the Middle Ages, was rebuilt as a citadel from the end of the 15th century. It served the Grand Dukes of Moscow until the 16th century and then the Russian tsars until the relocation of the capital to Saint Petersburg in the early 18th century. In the Middle Ages and early modern times, the Kremlin was the seat of the metropolitans and later patriarchs of Moscow. After the October Revolution in 1918, it again became the center of state power: initially the seat of the Soviet government, since 1992 it has been the official seat of the President of the Russian Federation. The name “Kremlin” is therefore also used as a synonym for the entire Soviet and Russian leadership.