ABSTRACT
The course of the Urban Revolution can be described as an ascending curve taking the alternative forms of a "ramp" or a "step". Rather than seeking to identify long-term developmental trends and cumulative aspects of growth, it visualizes the abrupt attainment of a new, urban level as being followed only by periodic recessions without successive further advances in level until the next phase of abrupt change. Both "ramp" and "step" are intended as polar abstractions rather than empirical descriptions, of course, so paradigmatic reconstructions combining aspects of both, like that suggested by curve B, in most cases may be historically more accurate. Phases of advance and decline during the latter part of the Urban Revolution, together with the exceptional size already attained by Teotihuacan very early in the sequence, argue against the simile of the "ramp".
