The caster conjures a wall of flame between them and their enemies for up to POW turns.

Creatures passing through the wall take 1d6+POW fire damage

The wall is POW meters tall, and Power meters wide.
The height of the wall may be doubled for 5 ep (once).
The length of the wall may be extended for 5ep per Power meters.
Additional energy may be spent to reduce the difficulty rating.
The spell may be maintained beyond the initial duration for 5ep per turn.

The wall may bend/turn, for example to form a circle/arch around the area.