It is said that the descendants of 21 emperors were given the surnames of Minamoto since the Emperor Saga (including the families which became extinct in the generations of the people who were given the surname themselves and in their children's generations).
嵯峨天皇以来、21代の天皇の子孫に源氏が与えられたと言われている（源氏を与えられた当人やその子の代で断絶・消滅した家も含めて）。