Portugal, the last of the six principal Christian States founded in the Iberian peninsula during the Middle Ages, is the only one to have preserved its independence at modern times.

Unlike the older kingdoms of León, of Castille, Navarre and Aragon, as well as old county of Barcelona, it was not built-in the State, initially fragile, but nevertheless durable, which became Spain.

The originality of the evolution of Portugal since XIIe century can be allotted neither to its former history, neither at the origin of the groups of population which constituted it, nor with its geographical composition, but rather with historical factors, in particular with the key function of certain characters and the succession of some major events which played a considerable part in the emergence of this new nation. Thus, Portugal - “field where the ground finishes and where sea starts”, Camoes said - is a clean entity, and that as of Antiquity.