The Kremlin is the symbol of first Russian and later Soviet power and authority. Its crenellated red brick walls and 20 towers were built at the end of the 15th century, when a host of Italian builders arrived in Moscow at the invitation of Ivan III the Great. Of the most important towers, the Saviour (Spasskaya) Tower leading to Red Square was built in 1491 by Pietro Solario, who designed most of the main towers; its belfry was added in 1624-25. The chimes of its clock are broadcast by radio as a time signal to the whole nation. Also on the Red Square front is the St. Nicholas (Nikolskaya) Tower, built originally in 1491 and rebuilt in 1806. The two other principal gate towers - the Trinity (Troitskaya) Tower, with a bridge and outer barbican (the Kutafya Tower), and the Borovitskaya Tower - lie on the western wall.
Within the Kremlin walls is one of the most striking and beautiful architectural ensembles in the world: a combination of churches and palaces, which are open to the public and are among the city's most popular tourist attractions, and the highest offices of the state, which are surrounded by strict security. Around the central Cathedral Square (Sobornaya Ploshchad) are grouped three magnificent cathedrals, superb examples of Russian church architecture at its height in the late 15th and early 16th centuries. These and the other churches in the Kremlin ceased functioning as places of worship after the Revolution and are now museums. The white stone Cathedral of the Assumption (Uspensky Sobor) is the oldest, built in 1475-79 in the Italianate-Byzantine style. Its pure, simple, and beautifully proportioned lines and elegant arches are crowned by five golden domes. The Orthodox metropolitans and patriarchs of the 14th to the 18th century are buried there. Across the square is the Cathedral of the Annunciation (Blagoveshchensky Sobor), built in 1484-89 by craftsmen from Pskov; though burned in 1547, it was rebuilt in 1562-64. Its cluster of chapels is topped by golden roofs and domes. Inside are a number of early 15th-century icons attributed to Theophanes the Greek and to Andrey Rublyov, considered by many to be the greatest of all Russian icon painters. The third cathedral, the Archangel (Arkhangelsky), was rebuilt in 1505-08; in it are buried the princes of Moscow and tsars of Russia (except Boris Godunov) up to the founding of St. Petersburg.
Just off the square stands the splendid, soaring white bell tower of Ivan the Great; built in the 16th century and damaged in 1812, it was restored a few years later. At its foot is the enormous Tsar Bell (Tsar-Kolokol), cast in 1733-35 but never rung. Nearby is the Tsar Cannon (Tsar-Pushka), cast in 1586. Beside the gun are located the mid-17th-century Cathedral of the Twelve Apostles (Sobor Dvenadtsati Apostolov) and the adjoining Patriarchal Palace.
On the west of Cathedral Square is a group of palaces of various periods; the Palace of Facets (Granovitaya Palata) - so called from the exterior finish of faceted, white stone squares - was built in 1487-91. Behind it is the Terem Palace of 1635-36, which incorporates several older churches, including the Resurrection of Lazarus (Voskreseniye Lazarya), dating from 1393. Both became part of the Kremlin Great Palace, built as a royal residence in 1838-49 and formerly used for sessions of the Supreme Soviet of the U.S.S.R.; its long, yellow-washed facade dominates the riverfront. It is connected to the Armoury Palace (Oruzheynaya Palata), built in 1844-51 and now the Armoury Museum, housing a large collection of treasures of the tsars. Along the northeast wall of the Kremlin are the Arsenal (1702-36), the former Senate building (1776-88), and the School for Red Commanders (1932-34). The only other Soviet-period building within the Kremlin is the Palace of Congresses (1960-61), with a vast auditorium used for political gatherings and as a theatre.