List of national monuments of Portugal
The national monuments of Portugal () were constructed throughout the Portuguese territory, and date back to the period of pre-historic settlement of occupation. Subsequently, the region that is today Portugal has been colonized by many civilizations, which have left marks in the territory, constructing markers, defensive structures, homes and places of worship to suit their requirements and means. The formal organization of the Portuguese state resulted in a process to qualify and quantify those structures that have had an intrinsic value to the Portuguese culture. Starting with the "Direcção Geral dos Edifícios e Monumentos  Nacionais (DGMEN)", and later by the "Instituto de Gestão do Património Arquitectónico e Arqueológico (IGESPAR)", the Portuguese government developed a registry of national monuments that includes a rich heritage of historical monuments throughout the country. This is a compilation of those structures that are designated as National Monuments only. History. The first documented peoples to occupy the western coast of Iberia were the "Ostrimni" recorded in Ancient Latin poetry, whose territory stretched from Galicia (in northwestern Spain) to the Algarve (southern area of Portugal). The Greeks called the area of Portugal Ophiussa, and its inhabitants the Ophi. The serpent-worshipping  Ophis are believed to have been a Celtic culture. These areas were eventually conquered, settled and assimilated by Indo-European peoples, made up of two probable invasions, the first by Proto-Celts who became the celebrated Lusitanians and the second by more developed Celts. Phoenicians also settled in trading posts along the coast and may have had contact with the assumably proto-Celtic Lusitanians, who, along with the Celtic Gallaeci, Celtici, Conii and Turduli became the base of the modern Portuguese ethnicity and culture. The Lusitanians along with the Gallaeci developed the Castro culture at the time of their invasion  by the legions of Rome. A formal organization of what would become Portugal began with the Roman occupation of the peninsula, which were responsible for re-purposing many of the castro settlements and moving the settlements from the hills to the valleys in the region. In the process, they constructed new buildings, established modern infrastructures (including internal water and baths) and a road network that connected Roman villas. Although there are many excavated ruins throughout the country, of particular importance are the Roman ruins of Conímbriga (Condeixa-a-Nova), in addition to many vestiges that encountered in the cities of  Lisbon or Évora. The disorganization in the Roman empire, which led to its fall, allowed the conquest by the Visigoths and the Christian Suevi in later years, along with other Germanic tribes. Many of the structures that survived this period include ancient churches and inscriptions built over previous constructions, which were the centre of Lusitanian settlements. Early Christian influences persisted for several centuries, until the Moors and Arab Berber peoples (from North Africa) invaded the Peninsula, including all of the territory which would eventually become Portugal. The Moors were first to construct many of the medieval castles that dot the  landscapes of Portugal. From the northern enclaves (Galicia and Asturias in Portugal's case), the Christian Reconquista began, expanding progressively south towards the southern coast of the Iberian Peninsula. This was not a permanent expansion, since the Moorish-Christian frontier continued to expand and retract for several years, with the victories and defeats of each battle. Meanwhile, Portugal became a county of the Kingdom of León and briefly during the independence of the Kingdom of Galicia in the 1060s and 1070s. It became an autonomous dominion of the Kingdom of León in 1128, emerging as a fully independent kingdom in  1139, officially recognized by the Treaty of Zamora in 1143. After this period, and with the rise of the Portuguese state after the beginning of the Age of Discovery, Portuguese architecture expanded under the patronage of the wealthy kings, nobility, powerful clergy and through the many battles with rivals such as Castile, the French and Dutch. During these periods, many of the prominent buildings were destroyed, rebuilt, re-purposed and closed on the whims of the monarchy, which progressively used architectural projects to support their power, remember past glories or expand their position in the Iberian peninsula. With the demise  of the powerful clergy and religious orders, and eventually the fall of the monarchy in Portugal, many of the once important buildings in the country were either reused as seats of governmental power, abandoned into ruin or reused as museum, although some remained places of public use (such as the religious places of worship). The 20th century movement to restore and preserve the architectural history of Portugal was initiated under the "Direcção Geral dos Edifícios e Monumentos Nacionais (DGMEN)" during the Estado Novo regime in order to inventory national treasures and preserve existing monuments. National monuments. Although there are numerous  monuments from various ages some of them have a special value due to their historical, architectural, artistic and cultural importance. These monuments are classified and protected by the "Instituto de Gestão do Património Arquitectónico e Arqueológico (IGESPAR)" ("Institute for the Management of Architectural and Archaeological Heritage"), which classifies national treasures in terms of several general criteria: historic and cultural, aesthetic and social, technical and scientific, but also includes issues of integrity, authenticity and exemplary importance. Owing to its relative value and importance, the cultural property may be listed as or national, public or municipal interest. In addition, these definitions are  also defined in terms of being monuments, groups of buildings or sites, based on existing international conventions. IGESPAR regularly proposes the listing of new assets based on its mission to safeguard national heritage. As time goes by, a wide variety of new buildings and groups of structures of varying typologies have been added to the national register of monuments, such modernist architecture, vernacular landscapes, archaeological sites, monastic buildings/structures, historical gardens, and more recently human-built business and industrial establishments. The listing process follows a strict procedure defined by Decree-Law no. 309/2009 (23 October 2009), which entered into force  in January 2010. IGESPAR also monitors and participates in the UNESCO registry of World Heritage Sites as a member state: there are 13 UNESCO World Heritage Sites in territory of Portugal. Similarly, eleven assets in the UNESCO world heritage list of 878 sites were former Portuguese possessions at one time, spread across three continents (Africa, America and Asia) associated with period of Portuguese Discoveries.