Some additional points of interest: Quake level designers could use "hint" brushes to help the BSP compiler determine where to create cells. Starting with Quake II, designers were able to place "area portals" which are portals programmers could toggle at runtime (think disabling a doorway portal when the door is closed).

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Edit: ugh, I missed dalant979's comment which already covers this https://news.ycombinator.com/item?id=42662830

Interesting. I recall Prey being the first game to hype portals for rendering, though I think theirs may have been for drawing not just culling? Does anyone know how it worked?

Dark Forces apparently also used portals for culling, IIRC.

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I remember the analogue to this in unreal engine 1, zones i believe, same concept though, good years.

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Some related content from Youtube channel "Matt's Ramblings":

Quake's PVS: A hidden gem of rendering optimization: https://www.youtube.com/watch?v=IfCRHSIg6zo

How Quake's software renderer ELIMINATES overdraw: https://www.youtube.com/watch?v=zdXsHWHxeBY

I added portals into software Quake: https://www.youtube.com/watch?v=kF-7Jd37gYk

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