Companion cavalry
Hetaeridia or Hetairidia () was a name of a festival among Macedonians and Magnesians (Athenaeus XIII. 572, quoting Hegesander). The origin of the Thessalian "Hetaeridia" is said to be related to Jason, who sacrificed to Zeus "Hetaereius", "Zeus of the Companions" (the Argonauts) 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).