From the Introduction:
Once upon a time, a nation decided to end the threat of the Tarrasque once and for all. An army was assembled, led by the greatest heroes of the age. Most importantly, a number of powerful magical weapons were created for the battle. The monster was lured into a tight canyon and the battle began.
At terrible cost, the Tarrasque was defeated. But not slain. It was impaled by fourteen special harpoons, the shaft made of an elongated immovable rod, each attached to a thick adamantine chain sunk deep into the canyon walls by magic. The Tarrasque was restrained.
A fortress, Taltasqa, was built around the Tarrasque, to watch over it. Every day its watchers hack away at the Tarrasque with powerful magic weapons to keep it weakened in case of escape. Even so, there are casualties as they misjudge its reach, or as its angry thrashing causes rock falls.
Thoughtless as a flood, a lightning strike, an earthquake, a brushfire, it doesn't cry out in fear, or pain, or frustration, only mindless rage. This behemoth ceaselessly struggles to free itself from the immovable harpoons. At first Taltasqa was wracked by constant tremors as it clawed away at the rock surrounding it, until all within its reach was ground to dust. Now it hovers unsupported like a grotesque levitating urchin. All that breaks the terrible silence in the canyon is the wet slither of its impaled limbs sliding back and forth along the harpoons that hold it and the occasional slap of its tail against a shaft. Its blood pools in the bowl it ground beneath itself with its own feet. The flensers must be lowered down onto the beast by chains that descend from a gantry just out of reach overhead.
Of course, being a powerful magical creature, the Tarrasque's blood, flesh and other body parts have certain useful properties. A side effect of keeping the Tarrasque imprisoned like this is a never-ending supply of powerful magical components. A city grew up around the fortress to house the various wizards, scholars and alchemists that came to exploit the Tarrasque's bounty. Eventually, it was almost as if the never-ending stream of Tarrasque blood, flesh, and bone was more important than imprisoning the beast itself.
The city is ruled by decadent nobles made nigh-immortal by their continued consumption of Tarrasque flesh. Warrior-butchers wield vorpal greatswords to hack away at the Tarrasque, and channels have been cut into the stone underneath the beast to channel the valuable blood away. The Tarrasque's distant screams and roars are a continuous background noise for the people in the city, with "tarrasque-quakes" common. An industry sprang up of ludicrously expensive magic items crafted from its body parts - tarrasquehide armor, tarrasquebone spears and potions and other alchemical miscellanea.
A delicate balance must be maintained, cut enough to support the populous, the research, and the economy, while leaving enough that the monster can never escape his prison.