PLU is Plumbing tech. In their creative madness, Civ 2 authors ( and i mean the very first version ) left this tech free in order to personalize other techs. By giving "Plu, nil," as prerequisite, you'll be able to forbid other civilizations to research what i call a "tribal tech"...
Maybe this will explain you better... go to my Classic Civilization Home Page , then download Antigonos scenario ( both versions, if you have FW, because graphic files are placed into MGE modpack), then take a look at Rules.txt file. Antigonids and their opponents, thanks to this trick, are able to build a peculiar tribal unit:
Antigonids) Flamethrower
Seleucids) Elephants
Tolemaics) cheapest ships
Lisimacids) Thracian light infantry... and so on.
Not to be mentioned that, by acting this way, you can create historical figures also ( but i don't want to waste the surprise...
).
[This message has been edited by Prometeus (edited December 10, 2000).]