Ambrosius Theodosius Macrobius

Sunt qui aestiment idus ab ove iduli dictas, quam hoc nomine vocant Tusci et omnibus idibus Iovi immolatur a flamine.

There are those who think that the Ides are named from the sheep belonging to the Ides, which the Tuscans call by this name and which is sacrificed on the Ides of every month to Jove by the priest.

Translation by Jane W. Crawford, © 2001.