Unlike the dynasties of northern China, which succeeded one another in rapid succession, the regimes of South China were generally concurrent, each controlling a specific geographical area. These were known as "The Ten Kingdoms" (in fact, some claimed the title of Emperor, such as Former Shu and Later Shu). Each court was a center of artistic excellence. The period is noted for the vitality of its poetry and for its economic prosperity. Commerce grew so quickly that there was a shortage of metallic currency. This was partly addressed by the creation of bank drafts, or "flying money" ("feiqian"), as well as by certificates of deposit. Wood block printing became common during this period, 500 years before Johannes Gutenberg's press.