Wikipedia
The Zygii or Zygians, were described by Strabo as a nation to the north of Colchis. He wrote:
And on the sea lies the Asiatic side of the Bosporus, or the Syndic territory. After this latter, one comes to the Achaei and the Zygii and the Heniochi, and also the Cercetae and the Macropogones. And above these are situated the narrow passes of the Phtheirophagi (Phthirophagi); and after the Heniochi the Colchian country, which lies at the foot of the Caucasian, or Moschian, Mountains. (Strabo, Geographica 11.2)
William Smith observes that "they were partly nomad shepherds, partly brigands and pirates, for which latter vocation they had ships specially adapted". They inhabited the region known as Zyx, which is on the northern slopes of the Caucasus east of Elbrus. To the east were the Avars, and to the west were the Circassians. To the north was Sarmatian territory, and to the south lay the part of Colchis inhabited by the Svans (Soanes of Strabo and Pliny the Elder).
Zyx in Greek literature referred to people inhabiting the area that is now occupied by the republics of Kabardino-Balkaria, North Ossetia-Alania and Checheno-Ingushetia. Confusingly, mediaeval Latin historians re-applied the term to those Circassians who formed a coastal federation in the sixth to eighth centuries A.D. This tribe also features in several ancient and medieval works, notably in Pliny (Zichoi), Constantine VII Porphyrogennetos, medieval Georgian chroniclers (Jikebi), Marco Polo, and Johannes de Galonifontibus, who, in his Libellus de notitia orbis, speaks of "Zikia or Circassia" and their language, perhaps the earliest reference to the Northwest Caucasian languages.
They were undone by invaders from the North, who possessed superior military technology - the Cimmerians and Scythians - in the 6th and 7th centuries BCE. It is notable that the term may have been used differently by the Romans, to describe a more westerly, ethnically Circassian people different from the people described in the earlier Greek documents.