Well, the outer walls, anyway - which are giant slabs of solid stone instead of individual brickwork mortared together. The interior construction was mostly more human scale before mostly razed. And then you've human-built Pavis right outside the walls, which is really a fair-sized town (and huge by Praxian nomad standards) but looks puny by comparison.
Visual aids really help with this one:
That's Pavis with all the buildings there, butting up against part of the Big Rubble's walls. Note where the newer walls and the Pavis temple half-pyramid come up to the giant-built fortifications, and the cultivated farmlands on cleared ground within it.
The overhead view helps too.
That's Pavis' street layout on the left. Big Rubble takes up most of the right map, with all of Pavis being that little dark nub sticking out to the northwest next to the river. You can also see the Troll Breach to the southeast, where they actually managed to collapse part of those monstrous walls.
One of the most distinctive urban areas in all of gaming.