Northeast of the volcano Hadriaca Patera, they visited a town that had been founded by Sufis. The original structure was built into the side of a canyon cliff, in a kind of high-tech Mesa Verde— a thin line of buildings, inserted into the break point where the cliff’s imposing overhang began to slope back out and down to the canyon floor. Steep staircases in walktubes ran down the lower slope to a small concrete garage, and around the garage had sprung up a number of blister tents and greenhouses. These tents were occupied by people who wished to study with the Sufis. Some came from the sanctuaries, some from the cities of the north; many were natives, but quite a few were newcomers from Earth. Together they hoped to roof the entire canyon, using materials developed for the new cable to support an immense spread of tent fabric. Nadia was immediately drawn into discussions of the construction problems such a project would encounter, which she happily told them would be various and severe. Ironically, the thickening atmosphere made all dome projects more difficult, because the domes could not be floated by the air pressures underneath them to the extent they once had been; and though the tensile and load-bearing strengths of the new carbon configurations were more than they would need, anchoring points that would hold such weights as they had in mind would be almost impossible to find. But the local engineers were confident that lighter tent fabrics and new anchoring techniques might serve, and the walls of the canyon, they said, were solid. They were in the very upper reach of Reull Vallis, and ancient sapping had cut back into very hard material. Good anchoring points should be everywhere.

No attempt was being made to hide any of this activity from satellite observation. The Sufis’ circular mesa dwelling in Margaritifer, and their main settlement in the south, Rumi, were similarly unconcealed. Yet they had never been harassed in any way by anybody, or even contacted by the Transitional Authority. This made one of their leaders, a small black man named Dhu el-Nun, think the fears of the underground were exaggerated. Nadia politely disagreed, and when Nirgal pressed her on the point, curious about it, she looked at him steadily. “They hunt the First Hundred.”