Saeculum obscurum (Latin: the Dark Age) is a name given to a period in the history of the Papacy during the first half of the tenth century, beginning in 904 with the installation of Pope Sergius III; it will last for sixty years until the death of Pope John XII in 964.

During this period, the Popes are influenced strongly by a powerful and corrupt aristocratic family, the Theophylacti, and their relatives.