The gods, or perhaps fate, always seem to take adjectives like "unbeatable" as challenges. For examples just see the Indomitable Tower (felled by undermining), Lord Morken the Unkillable (eaten by a roc), or the Neverburning Throne (burned). One has to wonder, then, just how long the 'Unbreakable' Wall will remain unbroken.
Running due west-east, from Drak Nev on the shore of the Nevrasea to Drak Sind near Sindal, the Unbreakable Wall marks the border between Khazarak and Kwal Dominion. The Wall is enormous: a hundred feet tall and thirty feet thick, lined on top by a broad walkway flanked by crenellated battlements. It is not made of individual stones, being instead a single solid construction of magical rock. The Wall is heavily resistant to damage, both magical and mundane, and can repair itself slowly over time. It even extends underground, to hinder tunnelling. Large towers are spaced every half-mile, with larger keeps every ten miles that house the only gates through the Wall. The Wall is home to an alert system designed by the Illuara, and installed by them for a surprisingly-cheap fee. With this system the Wall's defenders can quickly alert nearby sections to threats, and even (it is rumoured) pass on warnings as far as Stombarad itself.
The Unbreakable Wall was created eighty-two years ago. The pressure from the Dominion was intense, and the Iron Army of Khazarak was being steadily pushed back. Entire sections of the front were in danger of crumbling completely, and so the governing Nazak Council, with aid from the Concord of Runes and the Church of the All-Father, turned to drastic measures. They struck a deal, known as the Pact of Ezrin, with unknown entities, and the Wall arose from the ground literally overnight. However, the Pact came with a cost, and in that same night every dwarf who had made the Pact vanished without trace. Khazarak's leadership was gutted: every queen was gone, as were significant chunks of the hierarchies of both the Church and the Concord. It took quite some time for things to be stabilised again, but throughout all the turmoil Khazarak remained safe behind the Unbreakable Wall.
Originally the Wall was designed to meet with the northern border of Sindal, with Drak Sind securing its eastern flank and giving the army of Sindal an anchor point to base one end of their front around. The Dominion had other ideas, however, and over the next few decades steadily pushed the Sindai back, giving them the opportunity to flank Drak Sind and bypass the Wall altogether. At great expense, the new Nazak Council ordered the construction of a mundane wall, running from Drak Sind all the way south to the tip of the Spellscar, sealing off the only unfortified section of Khazarak's land border. This new wall (officially called the Flank Wall but commonly known as the Breakable Wall) is of standard dwarven construction: tough, sturdy, and durable, but paling in comparison to the unknown sorceries empowering the Unbreakable Wall.
The Final DutyPeering through arrow-slits, two dwarves looked down on the battlements below. All they could see, along the entire section of wall, was blood and death. Dwarves and hobgoblins fought each other, dealing out death with axe and sword. Periodically spells flew through the air as casters on both sides made their presence felt. It was not looking good for the dwarven defenders: there were too many foes, and they were unusually skilled. The Wall might soon be breached.
Even as the observers came to that conclusion, below them came a great crash as something was swung against a barred door. Again and again the crash came, increasingly accompanied by the sound of wood splintering. Then came one final crash, immediately followed by the sounds of hobgoblin warcries and dwarven battle-oaths. Two floors below the observers, fresh sounds of combat erupted, drowning out the muffled war outside. The two dwarves looked at each other, then at the sealed trapdoor leading down. It was sturdy, but they both knew it wouldn't hold. There was only one thing left to do.
As one, without saying anything, they turned to regard the object dominating the room: an arcane machine, bearing at its heart a huge crystal. The crystal was clear, perfectly transparent, but its facets broke up and distorted everything seen through it. It was perhaps four feet across, and rested in an ornate frame, with its point directly upwards. One of the soldiers laid his hand on it, and dramatically barked out a word. "Eluar!" Nothing happened. He looked at his companion, who replied to the unspoken question. "You didn't say it right! Eluar, like an elf would say it." The first dwarf tried again. "Eluar!"
The reaction was immediate. The crystal burst into a deep-red light that had both dwarves covering their eyes. A moment later a beam of light spiked up from the crystal's point, into the array of crystalline lenses directly above it. The lenses took the light, broke it up into a dozen strands, then somehow weaved it together again into a column both thicker and brighter than the initial beam. The column speared into the sky, rising as far as could be seen, a bright tower of red fully ten feet across, visible for miles. A few seconds later, to the east and west, similar beams of light pierced the heavens, but instead of red they were a bright blue.
Far away, in a complex buried deep within Stombarad, a small crystal on a map flashed bright red, and the occupants of the room burst into action. A dozen magical devices were grabbed, and a dozen voices began barking out orders to far-away strongholds. Across Khazarak, soldiers mobilised and began marching north.
Back in the tower, the sounds of fighting had died out below, and booted feet pounded on the stairs leading up. The two dwarves drew their weapons, and stood ready by the trapdoor. They said nothing, for what more could words do here? They had said the one word that needed to be said. All that remained was the final duty.