The treasury lay at Moria's lowest level, reached by a special tunnel the Dwarves had delved.
At the tunnel's end stood the vault door, forged of mithril alloyed with fine steel.
"This is the last intact treasury left in Moria," Balin said to Kael and Gandalf. "Its defenses are the strongest. All four walls are cast from mithril mixed with steel, and the door is locked by a password only Dwarves can speak. The orcs could not burrow into it, which is why this treasure was not plundered."
His expression tightened with old pain.
In the days of Khazad-dûm, enriched by mithril, wealth had poured in from every land, so much that one treasury could not contain it. After the Balrog awakened and Khazad-dûm fell, the demon cared nothing for gold, but the orcs were ravenous. They seized what they could, hoarded it, and even kept mining mithril, sending a steady stream to Barad-dûr to fill Sauron's war-chests.
Only the first treasury the Dwarves had ever built survived, for its defenses were too strong to break.
"I spent days cracking the vault's riddle," Balin added, a spark of pride returning. "Perhaps Durin's forebears foresaw the need and fashioned an impregnable vault, leaving us this hoard."
He swung the door wide and led them in.
Kael and Arwen stopped short, eyes wide.
Under torchlight, the treasury blazed. The chamber was vast, no smaller than a dwarf-hall, its center held by a massive golden pillar. The floor, walls, and ceiling were paneled in gold, and the room shone like a sunrise. Beyond that, mountains of coin and cut gems, jeweled work and ancient craft, filled the vault almost to the high roof.
It rivaled the Lonely Mountain's hoard by any reckoning.
More to the point, half this trove now belonged to Kael. In Erebor he had taken a tenth. Here, Balin had promised half of this vault to him at the outset.
Gandalf again declined Balin's wish to load him with treasure, taking only a purse of gold coins to lay in stores of Shire pipe-weed.
Kael had no such lofty detachment. He packed away half the vault with brisk efficiency. He had a household to keep, and beasts besides, not least a gold-loving dragon whose nest always wanted more coin and shine.
Balin's smile did not dim. Moria's true wealth was not gold and jewels, but mithril. Those veins promised treasure without end.
When they left the vault, Balin asked Kael to set a Floo connection in the First Hall's hearth, and offered payment for powder at a straight exchange: one gram of mithril for one gram of powder.
Kael shook Balin's hand at once. It was a bargain on both sides. He was already planning how to scale powder production without spending hours over each batch himself.
"Gandalf, Kael, there is one more matter," Balin said, hesitating. "You may not know this, but the mine's bottom, where the Balrog held sway, holds the richest mithril. If we are to keep mining, we cannot avoid it. The trouble is, since the Balrog's reign, the deep has become a field of molten rock, and it vents foul, sulfurous gas. We cannot get close."
He looked between them. "Could you go down and see whether the hazard can be cleared?"
Kael and Gandalf exchanged a glance. With the Balrog destroyed, the fires should have cooled—unless the demon had broken through into deeper magma.
Curious, they agreed.
They went to the mine's rim and descended on brooms. The shaft was very deep, not the world-cutting gulf of Durin's Bridge, but still plunging several thousand meters. The heat rose in odd waves as they dropped.
At the bottom, they found a river of molten rock, fountains of searing magma, and a stench like rotten eggs.
Kael cast Bubble-Head Charms to stop the poison air. Then he leveled his staff at the flow. "Aguamenti."
A flood of water poured out and deluged the lava. Steam billowed and wrapped the pit. As the water quenched the fire, the molten flow crusted and flashed to bright silver.
Mithril slag.
This was no ordinary lava. It was melted ore of very high purity. Wherever the surface cooled, the river set to a silver-white "Mithril Milky Way."
Even so, their eyes were drawn past all that glitter to a darker tunnel where heat seethed so fiercely that even torrents of water could not cool it. From there, mithril lava still welled up.
Gazing into the red throat, both knew it for what it was: the Balrog's lair.
The molten corridor breathed fire. Kael handed Gandalf a fire-protection draught. They drank, set their wards, and went in.
The passage plunged, cracked, and oozing, like a volcano's throat ready to blow. The heat would have melted the hardest steel. Without potion and magic, their bones would have charred.
Just as they wondered whether it truly led to the world's heart, the tunnel opened into a blazing chamber.
They had found it.
The cavern was a vast circle. Below, a lake of molten rock surged and spat, and in the middle a single black stone platform stood unconsumed, as if the mountain itself had raised an anvil for the demon to rest upon.
What stunned them most was the cave wall. Thick layers of red, translucent crystal had grown all around, turning the lair into a grotto of living fire. The crystals resembled the Balrog's core crystal, hot to the touch and saturated with fire-aspect magic. Because of them, the molten lake never cooled.
"What is that?" Kael asked, half in wonder, half in greed for knowledge.
Gandalf's eyes widened. "Flame crystals, formed under the Balrog's influence. It takes long ages for them to grow."
He smiled and clapped Kael's shoulder. "Your luck is excellent. Flame crystals are rarer and more precious than mithril. They can forge weapons bound to fire and grant great resistance to flame. An extraordinary material."
"Our luck," Kael said, grinning.
Gandalf chuckled. "Chip me a small piece for a tinder-stone, and keep the rest."
Seeing he truly wanted no more, Kael did not argue. He set to work, prying crystals from the wall with Aeglos and dropping them into a mithril box he had enlarged and warded. Even with potions, the crystals scorched his gloves. Any ordinary container would have burned through. Mithril alone held the heat at bay.
Gandalf joined him with good cheer, borrowing the Flammifer to free slabs from the face.
When they had taken every last crystal and sealed them in the chest, the heat in the chamber eased. From tens of thousands of degrees down to mere thousands. Still an oven, but less so. Without the crystals to feed it, the heat would decline with time, and the lake would cool to cold ore, though it might take decades, perhaps centuries.
They had promised to help. They would not leave it to time.
Together they cast freezing spells, locking the molten into solid stone. The temperature plunged. The slick rivers crusted and died back to rock.
Only when the flow ceased did they stop.
Gandalf picked out a small shard and rolled it in his palm. With a touch of the Ring of Fire's warmth, the crystal shed its perilous heat and became a deep red gem. He slid it into a pocket with a pleased nod.
"These formed under the Balrog's essence," he said. "They bear its stain. Remember to cleanse the taint when you return."
"How should I purify them?" Kael asked.
"The simplest way is the sun," Gandalf answered. "Lay them in sunlight, and the light will work, slowly. Your phial of Eärendil's Light is better. Use both, and it will go faster."
"I understand. Thank you," Kael said, and tucked the mithril chest away, already planning where in Lórien he would lay the crystals to catch both sun and star.