Aiantis () was a phyle of ancient Attica with six demes: Aphidna, Marathon, Oenoe, Rhamnous, Tricorythus and Phalerum. It was named in honour of Ajax the Great.
Marathon is located within the boundaries of this place.
It is attested by Plutarch that fifty-two members of the tribe of Aiantis died from wounds sustained in the Battle of Plataea.
The playwright Aeschylus came from deme Eleusis in Aiantis. His family were eupatrids.