Hetaeridia or Hetairidia was a name of a festival among Macedonians

Ancient Macedonians

The Macedonians originated from inhabitants of the northeastern part of the Greek peninsula, in the alluvial plain around the rivers Haliacmon and lower Axios...

 and Magnesians

Magnetes

The Magnetes were an ancient Greek tribe living in Thessalian Magnesia who took part in the Trojan War. They later also contributed to the Greek colonisation by founding two prosperous cities in Western Anatolia, Magnesia on the Maeander and Magnesia ad Sipylum.According to Hesiod's "Eoiae" or...

 (Athenaeus

Athenaeus

Athenaeus , of Naucratis in Egypt, Greek rhetorician and grammarian, flourished about the end of the 2nd and beginning of the 3rd century AD...

 XIII. 572, quoting Hegesander

Hegesander (historian)

Hegesander was an ancient Greek historian, and a citizen of Delphi. Besides an historical work, called Commentaries , which consisted of at least six books, and seems to have been of a somewhat discursive character, he wrote a work on statues...

). The origin of the Thessalian Hetaeridia is said to be related to Jason

Jason

Jason was a late ancient Greek mythological hero from the late 10th Century BC, famous as the leader of the Argonauts and their quest for the Golden Fleece. He was the son of Aeson, the rightful king of Iolcus...

, who sacrificed to Zeus

Zeus

In the ancient Greek religion, Zeus was the "Father of Gods and men" who ruled the Olympians of Mount Olympus as a father ruled the family. He was the god of sky and thunder in Greek mythology. His Roman counterpart is Jupiter and his Etruscan counterpart is Tinia.Zeus was the child of Cronus...

 Hetaereius, "Zeus of the Companions" (the Argonauts

Argonauts

The Argonauts ) were a band of heroes in Greek mythology who, in the years before the Trojan War, accompanied Jason to Colchis in his quest to find the Golden Fleece. Their name comes from their ship, the Argo, which was named after its builder, Argus. "Argonauts", therefore, literally means...

) and called the festival by this name. Athenaeus continues "and the Macedonian kings also celebrated the Hetairidia ". Scholars consider the Macedonian Hetaeridia an archaic festival and related to the Hetairoi (the name of the noble aristocracy and later Companion cavalry

Companion cavalry

The Companions were the elite cavalry of the Macedonian army from the time of king Philip II of Macedon and reached the most prestige under Alexander the Great, and have been regarded as the best cavalry in the ancient world and the first shock cavalry...

).