The Kingdom of the Dwarves has been rich and prosperous since the days that the first Dwarf-father awoke in the roots of the mountain. In the uncounted ages since he rose, the depths of the mountain have been carved into an intricate labyrinth of passages and palaces, workshops and dwellings, great halls and quiet chambers.
But, rumors of the golden treasure of the City-under-the-Mountain have reached the fire drakes of the north. Glori, the greatest of their kind, has set off to take this shining jewel of the Underworld for his own.
The Dwarven city is an expansive set of tunnels, great hall, and open spaces under the mountain. It is occupied by hundreds of thousands of Dwarves, and can field a large army of thousands. Dwarven warriors are sturdy, well armed and armored, and fire resistant. Dwarven axemen could damage or even kill a large fire drake, if given the opportunity to attack its vulnerable underside. Dwarven technology is equivalent to the high Middle Ages (~1300).
Fire drakes are long and thin, rather like snakes. They are winged and can fly, but they can also crawl through tunnels underground. Most passages carved wide and tall enough for dwarven pedestrian traffic can fit a drake through, even the great Glori. Drakes are as smart as humans, possibly smarter.
The drake's armor is largely impervious, although vulnerable in the face and underside. The face is not a good place to attack, because fire drakes, of course, breathe fire. If dwarves hid in a dwelling place with a door too small for the drake to fit through, the drake could cook the inhabitants of an average sized home with one breath.
Though there are few spaces large enough, Glori can fly inside the city in its biggest areas such the Muster Square and the Temple of the Stones.
The City-under-the-Mountain is ages old, older even than the drakes. But Glori himself is many thousands of years old. Though the dwarves might bar the great doors against him, there are many hidden and ancient passages under the mountain. Glori will eventually find a way in through a long lost tunnel; the dwarves must prepare to fight him inside their city.
Given the above information, what are the best tactics for the dwarves to assume to defend the City-under-the-Mountain against Glori?