The metropole (from the Greek metropolis for "mother city") is the homeland or central territory of a colonial empire. The term was mainly used in the scope of the British, French and Portuguese empires to designate their European territories, as opposed to their colonial or overseas territories.
The metropole of the Roman Empire was Italy. As the homeland of the Romans, it also maintained a special status which made it "not a province, but the Domina (ruler) of the provinces". Italy was federated by the Romans in the third century BC. Unlike the overseas and ultramontane territories conquered by the Romans, Italy, due to the presence of Rome in the peninsula, was not reduced to province status. Originally, Rome divided the Italics into three groups: Roman citizens, Latini (semi-citizens and semi-confederates), and socii (confederates). After 88 BC, all Italics were made Roman citizens. Italy continued to have this privileged status until 212 AD, when citizenship was extended to all the inhabitants of the Empire. From Caesar Augustus (27 BC) to Septimius Severus (192 AD), all Roman Emperors were Italics (Claudius, Trajan, and Hadrian, although born outside of Italy, came from Italic colonies and families). The term Ius Italicum identified the Roman Italian privileges, especially when it came to taxation, which could be extended to certain communities outside of Italy under certain conditions.
The metropole of the British Empire was the island of Great Britain; i.e. the United Kingdom itself. The term is sometimes used even more specifically to refer to London as the metropole of the Empire, insofar as the politicians and businessmen of London exerted the greatest influence throughout the Empire in both diplomatic, economic and military forms. By contrast, the term periphery referred to the rest of the Empire.
The historiography of British metropole-periphery relations has traditionally been defined in terms of their distinct separation, with a pronouncedly one-way, metropole-directed chain of command, communication, and control proceeding outward from the centre; the metropole informed the periphery, but the periphery did not directly inform the metropole. Hence, the British Empire was constituted by the formal control of territories, by direct rule of foreign lands, which were ruled by the metropole.
More recent work, starting with that of John "Jack" Gallagher and Ronald Robinson in the 1950s, has questioned the traditional definition, positing instead that the two were mutually constitutive and maintaining that, despite the apparent temporal inconsistencies inherent in their separate existences, each formed simultaneously in relation to the other. Gallagher and Robinson were socialists, observing the rise of the economic power of the United States in the developing world at a time when the African colonies of the British Empire were being granted independence; both scholars held that British and American expansion of overseas influence were ultimately developed along similar lines.
According to the theories of Gallagher and Robinson, the usage of soft power by the British, primarily through employment of British capital and other forms of economic influence allowed for the establishment of favorable economic relationships and free trade for goods which were manufactured in Britain. In doing this, Britain was able to gain the benefits of Empire without spending money on costly military affairs. In this interpretation, the "informal empire" of the British was a defining part of the metropole just as much as the "formal empire".
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In the scope of the Portuguese Empire, the metropole was the European part of Portugal, which included Continental Portugal (the mainland) and the adjacent islands (Azores and Madeira). It corresponded to the present territory of Portugal.
Until the mid 19th century, the Portuguese European territory was referred to as "Portugal" or as the "Kingdom". However, these terms became inappropriate when the Portuguese overseas territories gained the status of overseas provinces in 1832, and came to be considered an integral part of the Kingdom of Portugal alongside its European provinces. The use of the term "Metrópole" emerged then as the official designation of the European part of Portugal. From then on, and until the independence of most of the remaining Portuguese overseas territories in 1975, Portugal included the Metrópole and the Overseas.