Released in March of 1995 (over a year before Final Doom) 'Squares' is widely considered the first ever "proper" slaughtermap. It is said to have inspired the revered 'Deus Vault' WAD and was likely quite influential on the overall Doom scene. Would slaughtermaps have emerged the same way if not for Squares?

IWAD: Doom2
PWAD: 1squares.wad
Author: Costa Lappas
Get Squares here: https://www.doomworld.com/idgames/lev...

Ultra-Violence
100% Kills and Secrets (UVMax)
Pistol Start
No Saves
Keyboard controls only
Source port: PrBoom-Plus 2.6.2