From the 1920s to the 1980s, hundreds of people were buried in Red Square who were considered to be the most deserving sons and daughters of the Soviet state, that is, revolutionaries, heroes of the Soviet Union, statesmen and military leaders of the highest order. The burial in the Kremlin wall necropolis was in fact considered the highest posthumous honour that was reserved for only a few. A total of twelve statesmen - including Sverdlov, Mikhail Kalinin, Kliment Voroshilov, Leonid Brezhnev and Stalin, who was laid out in the mausoleum until 1961 - were buried in individual graves, and a large number of the revolutionaries rest here in a total of 15 collective graves. Most of the burials here, however, are niches in the Kremlin wall, in which over 100 urns with the remains of revolutionaries, heroes or main ideologues are walled. The people whose urns are in the Kremlin wall include, among others, Lenin's companion Nadezhda Krupskaya, the first cosmonaut Yuri Gagarin, the revolutionary writer Maxim Gorky, the nuclear weapon developer Igor Kurchatov, but also foreign politicians Clara Zetkin and Fritz Heckert.