This article is about the legendary creature. For the airplane control surface, see Aileron.
An avalerion or alerion is a mythological bird. It was "rather small, yet larger than an eagle" and lived near the Hydaspes and the Indus according to European medieval geographers and bestiaries, which were possibly based on a description by Pliny. Only two of the birds were said to exist at a time. A pair of eggs was laid every 60 years; after hatching, the parents drowned themselves.
The word's ultimate origin is unclear, possibly adapted from the German Adler (‘eagle’) or Adelar (‘noble eagle’). And it is found in 12th-century French as alérion and in medieval Latin as alariōnem (a large eagle-like bird).