Sixtus, the name of five Popes. S. I., St., Pope from 116 to 125; S. II., St., Pope from 257 to 259; S. III., Pope from 432 to 440; S. IV., Pope from 1471 to 1484; S. V., Pope from 1585 to 1590; of whom only two are of any note.
Definition taken from The Nuttall Encyclopædia, edited by the Reverend James Wood (1907)
Six Articles * Sixtus IV.