Written in the style of Guards! Guards! by Terry Pratchett:

It’s unclear why a band of desert nomads, migrating the ever-shifting paths of the Sand Sea for generations, decided to found a city in the middle of a rock canyon. Perhaps the oases dried up one year, or the morning dew failed to come, or maybe a slow-moving family chose to settle down and dig a well, rather than perish on the harsh desert march.

Whatever it was, water had something to do with it. Once you had a reliable water source, it fixed you in place, limited your range of travel so that with each passing season, the call of the desert became less and less alluring, and the call of sedentary civilization inversely more attractive.