This vault, built in the 1330s, is especially valuable as it contains gravestones with specimens of Bulgarian script. The writings were decoded in the mid-1800s by Husain Faihzanov, a professor of St. Petersburg State University. When Bolgar became part of the Russian Kingdom, Orthodox monks started using the mausoleum as a food storage cellar. By the time the restoration of 1968-1969 began, only the foundation, some parts of the inner walls and finishing had remained. The artists restored the top dome and the window apertures. An iron and claydite protective shell was then built over the structure.