Aeniania () or Ainis () was a small district to the south of Thessaly (which it was sometimes considered part of). The regions of Aeniania and Oetaea were closely linked, both occupying the valley of the Spercheios river, with Aeniania occupying the lower ground to the north, and Oetaea the higher ground south of the river. The boundaries of these two regions were formed by the arc of high ground running west from Mount Oeta round to Mount Tymphristos, then north round to the headwaters of Spercheios, and then east to the western spur of Mount Othrys. The lowland border in the Spercheios valley with Malis ran approximately north-south along from Oeta to the western spur of Othrys.