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 10th century, beginning with the installation of Pope Sergius III in 904 and lasting 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.