KonaKoder

lol, I only just understood your joke that for the portal cannon you could drop cannon-fodder creatures down the shaft. Shades of "Holy Grail"!

Thanks for that! I was going to talk about siege provisions moving through the ~~portals~~ Teleportation Circle, so good to know it's restricted on that.

Re. exploits from enemies, my idea is that there are 32 "Teleportation Circle Traps" that are isolated corridors with two permanent circles at either end, an "external" circle that is to be connected to the external environment and an "internal" circle that is connected to the Mustering Hall itself. So you have your highly disciplined troops moving at a precise jog go through an external->trap temp circle in 1 round before it closes and then mages in the Mustering Hall open another internal->trap temp circle. The thought is that if bad guys get into one of these traps, they still don't have immediate access to the citadel. (If I can figure out a good encounter for the players, I might trap them in one of these and throw in a "can be flooded" vs. maintenance tunnels or air shaftts, maybe a passage above with murder holes, etc. But if I can't do something with it, it's just going to be dungeon-dressing and its okay if it's not 100% logical.)

Re. "creatures only": Do you have a reference for that? I assume it's "creatures and possessions" and not "Terminator"-style naked?

Well, the premise is that the BBOG is aware and paranoid of magical overthrow and does everything in its power to discover and "re-educate" or kill casters. They have a Stasi-like "Magisterium of Arcana" with a monopoly on spell books and rare components, informers and spies, etc. The party time-traveled back to this era and even the 6th-level Cleric, Warlock, and Sorcerer (in particular) would be considered major threats and are being pursued by a Hans Landa-esque character who knows they exist, but no details. (Kind of off-topic, but it's been a really fun couple of sessions at the table developing this... :-) )

Yes, it's the idea of permanent tele circles.

"Velocity is matched with the destination" : that makes sense, but do you have a citation?

The character's are time-traveling, are only 6th level, and a single permanent tele circle takes a year, so I'm not fretting too much about being exploited by the players. Plus, it's a good group so I think we'd work it out.

Yes, exactly.