The Roman Empire, which grew out of a city-state, required effective structures for its administration and defense as it expanded massively. The provinces served as this instrument, the central unit for administration, justice and legal proceedings, tax collection, and military matters. Gabriele Wesch-Klein describes the historical development of the provincial system from the first province, Sicily, which was conquered in 241, to the highly complex system of late antiquity with up to 120 provinces under Diocletian. She outlines the hierarchical administrative structure and the various areas of responsibility. She analyzes the military significance of the provinces for the extensive rule stretching from Gibraltar to Syria and from England to North Africa. Additionally, she traces the economic importance for the financing of the empire and describes the situation of the local population.