Since I cannot get the search feature to work, I will ask my question of the great community here.
Does it say anywhere what the magical effects of the Basalt Bastions are? I would suppose it prevents some type of teleportation and could possibly harm demons who come close to it, but I have no documentation on this (that I can find).
Nothing official on the effects of the basalt bastions. But what you describe is basically what I gave it. There was also an effect that blocks demons from simply flying over it.
ps cool user name
I had it block all teleportation (unless someone with the blood of Spellmason was present) as a passive ability. Doing some research in the library of the Chisel, it was possible to find some references to the active powers of a "fear" that affected demons (likely only babau will be affected) and an auditory illusion that allows the active caster to be heard a mile or two away by a crowd.
These 2 active powers were used to great effect during the Seige.
The teleportation limitation made the Scion of Spellmason important and forced the babau (the majority of the demon forces) to climb across the canyons. I allowed flight over the wall, making the vrocks a strike force that would delay the defenders while the babau moved into position.
IMC, I used an much altered version of The Battle of Red Gorge.
The main power I gave the Bastions is to forbid entrance in Redgorge to all demons, until peace reigned in the village.
Of course, as soon as Cauldronites did attack Redgorge to capture the Chisels (Maavu fled from Cauldron riots), the demons took notice and Nabtathoron quickly led its troops against Redgorge.
The secondary power of the Bastions is to annihilate demons which come to close to them (15 feets or so). Black filaments would emanate from the jet-black Bastions and cocooned the demon, shrinking it into nothingness in a couple of rounds.
Nabtathoron did knew the trick, however, and devised a special ritual involving several Babaus to withstand the Bastions power, allowing himn to lay waste freely near the Bastions.
That made for a nice tactical battle under the Bastions shadows (which still protected against the lesser demons), which my PCs managed to win by having the Chisel resources (golem and winged statues) attack and destroy the Babaus, so reducing Nabtathoron's protection, then hitting him with a 3-charges shot from a Ring of the Ram which sent Nabtathoron against the Bastions.
The Bastions recognized their old, bitter enemy, and tried to annihilate him, however I allowed him to escape to use it again when the PCs found Alek Tercival (IMC the Redgorge battle happened earlier).
The Bastions now sports a completely transparent, large winged demonic silhouette were Nabtathoron hit them, and several narrow transparent cracks where the filaments sprout from. People in Redgorge look at them as a strong reminder to keep peace in their village.
Ciao
Marco
As most here did, I had 'em prevent teleportation but allow flyovers. They also had the special power of discharging "holy lightning" on nearby demons for each segment of the wall manned by a trained individual.
I used Nib's Redgorge Seige which gave victory points for training in bastion defences as well as the areas he documented. Training of the bastion operators was up to the Chisel, but all delays in the assault created by the party gave them more time and hence upped the VP. That was more of an effect on the siege than the lightning per se (it was limited to one attack per round), but the lightning gave a nice visual effect during the battle itself.
I required trained operators to make the walls less of a deus ex. There were many more bastion segments than operators, so the challenge getting those vital individuals to the correct defensive positions quickly and protecting them from attack added some suspense and urgency. The limited number of functioning segments prevented the walls from being the star of the show instead of the party. And "lightning's" ability to do damage to demons surprised and delighted my experienced and somewhat jaded party, which was a nice bonus.