To my knowledge, no such chart or table has been published. The only known fort part value is 16: iron gate, which is the only fort part value actually used in the game's ritual data. Others may exist, but you'd have to figure them out through trial and error, and wall may or may not be one of them.

Have you tried using:

terr -31 # walls

instead? Unless there's some reason that doesn't work for you, it would be a simpler solution.

Thank you Colonel Dracula joins the Navy

I just did the trial and error, and the answer turns out to be bit flags in the order found in the modding guide. The fun part was the logic puzzle --- for example, a ritual with fortreq 4 can be cast in a Necromancer's citadel but not a Demonologist's citadel, therefore 2^2 means widebattlements.

1 walls
2 highwalls
4 widebattlements
8 woodengate
16 irongate
32 enchantedgate
64 extracover
256 widegate
512 cavewalls

None of the existing terrain types use 128, which seems to correspond to the manual's statement "sidegates This command is not used in the game and probably won't work."

You can combine multiple bit flags in a single test, but the sense is always AND, rather than OR. For example, if your ritual says "fortreq 6", it could be cast in a location having both high walls and wide battlements (Warlock), but not a location having only high walls (Witch) or only wide battlements (Priestess). If you say fortreq 0, however, the ritual can be cast anywhere.