Why are the walls in Doom fully 3D, but enemies can only be rendered as 8-directional sprites?

Question

I’ve read that enemies in Doom are rendered as sprites because of hardware limitations. But why is it that walls, stairs, etc. appear fully 3d by contrast?

[example](https://www.youtube.com/watch?v=tDmf9dgso84)

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In: Technology

Answer 1

Each surface is 4 points. Constructing a realistic monster would take dozens or over a hundred points which would have maxed out the memory required to display them and they would have looked pretty blocky.

Each of those points would have to be stored and manipulated every time the monster moved. Remember that when doom came out, we only had 4 MB or less of memory.