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.