In this particular case, it’s easiest to start off with an example.
The peaceful villages of Ridmarch have nestled in the folds of the hills beneath the mountains for many centuries, their inhabitants living by herding, sheep and goats, farming the hillsides, and cutting wood from the stands of pine.
Centuries past, a small humanoid army, sworn to destroy the Ridmarches and to claim the land for their own peoples, swept down from the mountains in the night. Led by one “Harkold” (actually a minor demon possessing the body of a foolish would-be summoner) they overran Viardel, the first hamlet in their way, with no more disturbance than a few screams as houses were surrounded and stormed. With Viardel silently fallen, there was no obstacle or guard between them and the town of Kareon in the central vale. If they took that central valley, the other villages of the Ridmarch – now isolated and unable to support each other – would be easy prey.
In the hills above Viardel, a young shepherd boy had been hunting late for a lost ewe and her lamb – and so was spared when a detachment of scouts set fire to the sheepfolds and cut down the other shepherds as they tried to escape.
Rather than fleeing into the safety of the woods and hills, that courageous youngster slipped into the temple overlooking his ravaged village – and his slain family, friends, and neighbors – and there used the temple bell to sound the alarm. Whether the ensuing fire was also meant as a warning beacon may never be known, but the youngster paid a terrible price for his valor, pinned beneath the fallen bell and left to burn alive.
Roused from their slumbers early enough, the hastily-assembled militia of Kareon and its farmers held the walls – albeit at a great price. Early the next morning the massed militias of the other villages of Ridmarch struck at the attackers rear flank, and two local adventurers attacked “Harkold”. Those battles were hard-fought – but eventually ended in a massacre of the enemy. The bodies of the enemy slain were thrown into a nearby cave, a minor sacred relic – the Eagle of Ridmarch – was placed within, the entryway was sealed with a great slab of stone, and priestly ceremonies were enacted to ensure that their dark spirits would never rise to trouble the Ridmarches again.
When the grateful survivors reached the remains of Viardel, they found the body of an adolescent boy broken beneath the warning bell, burned beyond recognition, and now – with the death of the people of Viardel and the destruction of the temple records – forever anonymous. They raised the bell to hang once more in the tower of the ruined temple and left a memorial there, in honor of the young and nameless sentinel who had died to save them.
When, twenty years later, a sizable party of bandits emerged from the mountain forest to raid a resettled Viardel, the unattended bell sounded a warning once more – and the legend of the nameless sentinel grew. It remained a popular tale for several centuries and then, when the Ridmarch Vales were well within the frontiers of civilization, faded along with the need for vigilance.
When the ancient belltower collapsed some centuries later, none remarked it.
When a minor earthquake cracked a weathered slab of stone, and sent half of it’s blurred priestly inscriptions toppling down a slope and into a nearby gorge, it passed unnoticed.
When a passing adventurer fought a few minor undead and took an relic from the cavern in the woods that the slab had once sealed (and later sold it to a collector of arcana) it caused no disturbance.
But with that, “Harkold” took notice. Over the centuries he had slowly risen through the ranks of demonkind until he was a minor demon no longer. Now an Archdemon, or even a Lesser God of Evil, he saw an opportunity to spread suffering and destruction – and to avenge an ancient grudge. He dispatched some of his cultists to the area to settle in, gather power, and perform a ritual to open a path for him. What was another twenty years to a prince of darkness?
On a night of the winter solstice, when the powers of light were at their lowest ebb, the earth shook again as terrible sacrifices were offered in the depths of the old burial cave. A rift opened – and the foul energies of the infernal planes bubbled up. Ancient remains, infused with hellish power and once more linked to the souls that had once animated them, gave birth to a dark legion.
That legion set forth once again. This time, perhaps, they would fulfill their oath – and the Ridmarches would become a haven for the humanoids who still lurked in the depths beneath the nearby mountains.
The cultists received the first portion of their reward – command over a few units of the dark legions, giving them minions to work their wills in anticipation of their high positions to come when the Ridmarches had become a realm of darkness.
Those units struck at the cultists personal targets – avenging slights, destroying enemies and those who suspected the cultists secrets, and gathering wealth and slaves for their masters.
When the dark legion’s scouts struck at nearby farms and hamlets, many died, their souls stolen and bound to the rift to help maintain it. Some few fled successfully – and a priest attempting to sound the alarm discovered that the ringing of bells on sacred ground could hold the dark legion at bay.
Still, the situation is desperate. While having everyone hide in those small areas that can be protected is a stopgap measure, it makes farming near-impossible. All too soon the people of the Ridmarches will begin to starve. Even now, the undead have began to set fires that spread into protected areas, to raise or break dams to flood them, to lay traps on the routes to and from them, and to slaughter livestock and trample crops. They pick off stray children, those who are unable to reach shelter before sundown, and travelers on the roads.
Worse, until their oath is satisfied, or ended with the breaking of “Harkold’s” power, the dark legions can never be truly slain; they are merely than infernal constructs controlled by souls already dead and on the lower planes. When destroyed they will simply rise again at sunset – and so “killing” them is only worth about 20% of the normal experience (and none at all after you do it five times). However, as the sounding of a bell once brought destruction on them, so they can be held back or even temporarily dispatched by the sound of bells combined with sacred energies. Worse, of course, they cannot be prevented from reporting what happened the next morning; the dark legions will steadily become more familiar with, and prepared for, the tactics of any group that fights them too often.
The game statistics of the dark legions can best be represented by various kinds of corporeal undead. The legions, however, are all intelligent regardless of their basic statistics; they will learn and use basic tactics. Any which could normally reproduce themselves, however, will only be able to spawn basic animated corpses unless they possessed the magical ability to create more powerful undead in life and apply those talents. Fortunately, they cannot directly attack any consecrated area while bells are ringing within it, and any priest attempting to drive them away or exorcize them will gain a substantial bonus if bells are ringing nearby while he or she does so. Unfortunately this does not prevent them from making indirect trouble – and, as noted above, any form of “destruction” that cannot cross the dimensions and strike at the lower planes, is strictly temporary. Even – say – burying them in concrete is only good for a month or so, after which the link with the soul in the lower planes will break and they’ll create a new body back at the rift.
Like many undead, they are also driven off by the light of the sun – but can readily take refuge underground or within structures.
Olfenac: This small town lies at the entrance of a mountain pass that has become one of the major trade routes for the area. It’s relative wealth, easy acceptance of strangers, and location near the Cavern of the Dead, made it the natural spot for “Harkold’s” cultists to infiltrate. At the moment, it’s completely dominated by demon cultists, who have used their new minions to kill or capture the rest of the population – and to help turn the cellars, and a few natural caverns below the town, into a considerable network of tunnels in which to hide their minions, keep their slaves, and conceal their new wealth. They have kept one (very!) elderly priest to front for them; the poor old man is senile enough to be unaware that the occasional night of gathering in his small temple and ringing the bells is purely for show. Alert characters, however, may realize that all the nearby graveyards have been pillaged in search of material for more undead – and for any minor treasures that might be found. The fact that none of the current residents has lived in the area for more then five or six years may also serve as a warning.
The cultists of Olfenac are currently beginning to expand their operations a bit. More people to sacrifice means more power and rewards, the occasional caravan disappearance is only to be expected at the moment, and lone travelers are at risk in the best of times – and if some party of adventurers is foolish enough to believe that the villages small (and desecrated) temple is proof against their undead minions just because some bells are ringing… well, they deserve their fates.
Olfenac, of course, is a fairly basic “dungeon”; the cultists are decent ritualists, and use ritual effects to cover up inconvenient details such as their evil auras, but their active magic is fairly basic – unless they’ve earned a temporary boost through some exceptionally good sacrifices. They are, however, kept informed of relevant information gathered by the Dark Legion and it’s scouts – so if a particularly powerful group of adventurers is in the area, they can upgrade their magic with special sacrifices, their tunnel-defenses with better traps and a few summoned demons, and their personal abilities with some gift from their patron – most likely some version of Lycanthropy.
If the cultists are exposed and defeated, there is enough information here to easily locate the Cavern of the Dead and to get an idea of what ritual they used to open the rift. If enough of them are captured rather than slain, enough details of the ritual can be extracted to attempt a relatively easy counter-ritual. If not, a more general – and far more difficult – ritual may be used to seal the rift – and, if the rift is so sealed, the remaining elements of the Dark Legion will fall to dust at sunrise, not to arise again – unless another group of cultists manages to re-establish the rift.
The Dark Legion – and the cultists – are well aware of this particular vulnerability, and have left guards within the Cavern of the Dead who will resist attempts to enact such a sealing ritual.
The Fallen Belltower: Hidden in an overgrown patch of hills overlooking old Viardel a few fragments of walls and a heap of rubble are all that remain of the once-temple of Viardel, and later the Shrine of the Nameless Sentinel. Whether that once-consecrated ground retains enough holy power to protect those there from the Dark Legion through the ringing of bells is up to the game master.
While the temple crypts were never extensive, there were several rooms beneath the old temple, and the heavy bell has – of course – long since fallen through the old floor and into the basement. While no undead were ever tolerated there, it’s quite possible that – over the years – something nasty has moved in.
If the bell is dug out, hung, and once more rung, it will once again herald the defeat of the dark legion, as it did so many centuries ago. The rank and file will simply fall to dust, banished forever from the mortal plane. The greater beings – the captains and commanders – will be stripped of their special defenses and their immortality, while remaining subject to all their limitations – and when they are slain, they too will be forever banished.
Sadly, there are few in Ridmarch who so much as remember the tale of the Nameless Sentinel, much less the location of the shrine and the blessed bell. Locating the bell will require a good deal of digging into the origin of the Dark Legion, talks with old (and desperately busy) priests and the occasional historian, traveling the countryside to reach distant temples where records are preserved while evading the undead scouting parties, and bargaining with desperate folk. Still, this route to victory doesn’t call for much personal power – or much fighting. Just research and cleverness.
The Cavern of the Dead: This minor cavern complex includes half a dozen accessible chambers, several pools and streams, a selection of passages (most of which dead-end), the remains of many bodies, a partially sealed-off chamber dedicated to totemistic shamanic magic (it’s pent-up energies, amplified and tainted by the abyssal forces unleashed in the rest of the complex have turned the chamber into a gateway to a terrible world filled with dinosaurs and other primordial creatures; hopefully the Dark Legion has not discovered these and turned them to their own purposes), and the rift to the abyss – hidden beneath a roiling pool of boiling, unholy, corrosive fluid. From it rise new bodies for the Dark Legion, through it passes the influence of the Dark Legions controlling souls – and beyond it lies the heart of “Harkold’s” demonic realm.
Truly epic-level characters may wish to force their way though the rift and confront “Harkold” and his forces directly – ending the oath and curse with the destruction of the archdemon who empowers both. In general, good luck with that… Such a course of action will require truly immense power – and will incur the enmity of other forces of darkness, for none will bear such an intrusion in their domain with good grace, no matter what their rivalry or enmity with “Harkold”.
Casting the Eagle of Ridmarch into the gateway will seal it, causing the Dark Legion to revert to mere masses of infernal slime and ooze. While still a filthy, toxic, mess to clean up – and likely to turn any normal creatures it contaminates into fearsome, infernal dire creatures – this isn’t an especially widespread menace.
Reconstructing and resealing the sealing slab is a strictly temporary measure; it will prevent “slain” and reborn members of the Dark Legion from exiting the Cavern – but unless it’s supported by the presence of the Eagle of Ridmarch (either inside or outside) the Dark Legion will be able to break the slab’s enchantments eventually.
Rathine Mora’s House: Rathine is an elderly (if low-level) bard and a collector of the tales and mementoes of the Ridmarches. If asked, he can provide a reasonably accurate version of many local tales – including the tale of the Unknown Sentinel. Unknown to him – although recognizable by a knowledgeable priest who has been studying the ancient records- his collection includes a powerful sacred relic, the Eagle of Ridmarch. This particular item was forged around a minor divine token from a local god of war, and, many centuries ago, served as a rallying standard for the ancient militia of the region. After the battle it was used to help seal away the spirits of the attackers – but it had also become a focus for the strength and valor of all the militiamen who had fallen in the defense of Ridmarch. While the eagle is displayed, no defense against the enemies of Ridmarch will fall – although, of course, individual defenders may. They will not, however, do so easily.