In 1930s, Soviet researchers discovered a copy of a 10th-century waqf document (copied around 1568) that specified that Ismail Samani donated Bukhara's cemetery Naukanda land for what appears to read as a funerary building for his father, Ahmad, confirming earlier assumptions of a dynastic nature of the monument. Before the time of Genghis Khan's siege and sack of Bukhara in 1220, the mausoleum is believed to have been buried in mud and sand from flooding and landslides, remaining so for centuries. Thus, when the Mongol armies reached Bukhara, the tomb was spared from their destruction, unlike most other buildings of that era. For the same reasons, the building was not known to the world until the early 20th century when archaeologists rediscovered it.