"How many people do you think there are in Nessus?"
"I have no idea."
"No more do I, Torturer. No more does anyone. Every attempt to count them has failed, as has every attempt to tax them systematically. The city grows and changes every night, like writing chalked on a wall. Houses are built in the streets by clever people who take up the cobbles in the dark and claim the ground - did you know that? The exultant Talarican, whose madness manifested itself as a consuming interest in the lowest aspects of human existence, claimed that the persons who live by devouring the garbage of others number two gross thousands. That there are ten thousand begging acrobats, of whom nearly half are women. That if a pauper were to leap from the parapet of this bridge each time we draw breath, we should live forever, because the city breeds and breaks men faster than we respire. Among such a throng, there is no alternative to peace. Disturbances cannot be tolerated, because disturbances cannot be extinguished. Do you follow me?"
"There is the alternative of order. But yes, until that is achieved, I understand."
Two gross thousands is 288,000. Assuming the same homeless rate as New York City, that makes the population of Nessus about 100 million. Even taking into account the fact that Nessus is a decaying city in a backwards era, so the homeless rate might be higher than estimated, it is still obviously a huge city.
A brief word on names: Later in the book, someone tells a story about the city, saying "It was not called Nessus then, for the river was unpoisoned." Nessus was a centaur in Greek mythology that attempted to rape Hercules' wife Deianeira. Hercules shot him with a poisoned arrow. "As a final act of malice, Nessus told Deianira, as he lay dying, that his blood would ensure that Heracles would be true to her forever." "Later... she spread the centaur's blood on a shirt and gave it to her husband." A bloody shirt? For me? You shouldn't have! Anyway, he died due to his poor fashion sense. So the city is called Nessus because of the poisoned river that flows through it, Gyoll.
The river Gyoll (Gjöll) is a river in Norse mythology that you have to cross to get to the gate of the underworld Hel. "The river is said to be freezing cold and have knives flowing through it." Nessus' Gyoll is very cold, but no knives that I know of (except from the cold). The Norse Gyoll has a Greek counterpart, the river Styx. Some legends said that Styx was "so foul that to drink of it brought instant death." It's interesting how the different cultures describe the river of death. The Norse describe it as freezing cold, since falling into a freezing river was probably a common and horrible way to die. The Greeks, who obviously had no experience with anyone freezing to death in their rivers, made it poisonous, since unlike the Norse they didn't have ultra-pure glacial runoff to drink, so there was probably a chance of dying from bad water.
Anyone that has an idea of what "the alternative to order" is, let me know.