The menologem (Ancient Greek: μηνολόγημα, mēnológēma), menologium (Latin), or menologion (μηνολόγιον, mēnológion) was a dating clause used in certain types of official acts of the Byzantine Empire, such as the prostagma and sigillion.
The emperor alone was allowed to write the menologem in red ink, while the Patriarch of Constantinople was permitted to use black.
[1][clarification needed] The earliest use of the menologem dates from the reign of Constantine IV (654–85).
For example, on 5 August 1243 the Latin emperor Baldwin II authenticated a letter by writing a dating formula with his own hand in red ink, but he dropped the indiction and added to the day the year of the Lord, the place of signature (Constantinople), and his regnal year.
Among the Byzantine successor states after 1204, the authentic red menologem of the emperors was kept alive only in the Empire of Nicaea.