Cyrillus, Greek jurist of the 5th century, was a professor in the ancient law college of Berytus (present-day Beirut), and one of the founders of the oecumenical school of jurists (της οικουμενς διδασκαλοι). This school preceded the succession of Anastasius to the Eastern empire (AD 491), and paved the way for Justinian's legislation.

Cyrillus is a lunar impact crater located on the northwest edge of Mare Nectaris. Intruding into the northeast rim is the equally-large, and younger Theophilus crater. To the south is another prominent crater named Catharina.