The Arimaspians were a tribe of one-eyed men who lived at the foot of the Rhipaion Mountains (probably the Carpathians) in northern Skythia. They were constantly at war with the gold-guarding, griffins.
The Arimaspians were described by Aristeas of Proconnesus in his lost archaic poem Arimaspea. Proconnesus is a small island in the Sea of Marmora near the mouth of the Black Sea, well situated for hearing travellers' tales of regions far north of the Black Sea. Aristeas narrates in the course of his poem that he was "wrapt in Bacchic fury" when he travelled to the north and saw the Arimaspiansans, as reported by Herodotus.
"There is also a story related in a poem by Aristeas son of Kaüstrobios [Greek poet C7th B.C.], a man of Prokonnesos. This Aristeas, possessed by Phoibos [Apollon], visited the Issedones; beyond these (he said) live the one-eyed Arimaspoi (Arimaspians), beyond whom are the Grypes (Griffins) that guard gold, and beyond these again the Hyperboreoi (Hyperboreans), whose territory reaches to the sea. Except for the Hyperboreoi, all these nations (and first the Arimaspoi) are always at war with their neighbors; the Issedones were pushed from their lands by the Arimaspoi, and the Skythians (Scythians) by the Issedones." - Herodotus, Histories 4. 13. 1
"Of these too, then, we have knowledge; but as for what is north of them, it is from the Issedones that the tale comes of the one-eyed men [Arimaspoi, Arimaspians] and the Grypes (Griffins) that guard gold; this is told by the Skythians (Scythians), who have heard it from them; and we have taken it as true from the Skythians, and call these people by the Skythian name, Arimaspoi; for in the Skythian tongue arima is one, and spou is the eye." - Herodotus, Histories 4. 27. 1
Battles between griffons and warriors in Scythian tunics and leggings were a theme for Greek vase-painters. Spiritual descendants of the one-eyed Arimaspians of Inner Asia may be found in the decorative borderlands of medieval maps and in the monstrous imagery of Hieronymus Bosch.
Tadeusz Sulimirski (1970) claims that the Arimaspians were a Sarmatian tribe originating in the upper valley of the River Irtysh, while Dmitry Machinsky (1997) associates them with a group of three-eyed ajna figurines from the Minusinsk Depression, traditionally attributed to the Afanasevo and Okunevo cultures of Southern Siberia.  Mythological background
Cheremisin and Zaporozhchenko (1999), following the methodology of Georges Dumézil, attempt to trace parallels in Germanic mythology (Odin and the mead of poetry, the eagle stealing golden apples of eternal youth). They hypothesize that all these stories, Germanic, Scythian, and Greek, reflect a Proto-Indo-European belief about the monsters guarding the entrance to the otherworld, who engage in battles with the birds conveying the souls of the newly dead to the otherworld and returning with a variety of precious gifts symbolizing new life.