Erriapus /ɛriˈæpəs/, or Saturn XXVIII (28), is a prograde irregular satellite of Saturn. It was discovered by Brett Gladman, John J. Kavelaars and colleagues in 2000, and given the temporary designation S/2000 S 10.^[7][8] It was named Erriapo in August 2003^[9] after Erriapus (also rendered Erriappus), a giant in Gaulish mythology; the name was changed from dative Erriapo to nominative Erriapus per IAU conventions in late 2007.^[10][11]

Erriapus is about 10 kilometres in diameter, and orbits Saturn at an average distance of 17.5 Gm in 871 days.

As a member of the Gallic group of irregular satellites, which share similar orbital characteristics and a light-red colour, Erriapus is hypothesized to have its origin in the break-up of a common progenitor of the group,^[6][12] or to be a fragment of its largest member, Albiorix.^[13] It has a rotation period of 28.15±0.25 h, and is thought to rotate on its side, giving it similar seasons to those of Uranus.^[14][15] With a fairly elongated shape, it is a candidate for a contact binary or binary moon.^[4]