The era between the death of Charlemagne and the close of the
Carlovingian dynasty is so called from its almost ceaseless wars. It is
sometimes called the leaden age for its worthlessness, and the dark age for its barrenness of learned men.
The age of cruelty and hard-heartedness. When Hubert tells Prince
Arthur he must burn his eyes out, the young prince replies, “Ah, none
but in this iron age would do it.” (Shakespeare: King John
Source: Dictionary of Phrase and Fable, E. Cobham Brewer, 1894