Castles in Portugal were crucial components of the military throughout its history. The Portuguese learned the art of building fortifications from the Romans and the Moors. The Romans, who ruled and colonized the territory of current-day Portugal for more than four centuries, built forts with high walls and strong towers to defend their populations. The Moors, who invaded the Iberian Peninsula in the year 711 A.D., brought new stonework and heavily fortified gates to the peninsula.
History
Portugal has well-defined geographic boundaries, with the Atlantic Ocean to the south and west, and rivers and mountains to the east and north. It occupies the westernmost portion of the Iberian Peninsula and is about the size of the American state of Indiana. The country is a place of topographical contrasts, making defense difficult. The areas around Porto in the north are covered in green hills, with fertile river valleys and a rocky coast. The green mountains are less fertile as they spread to the east and become mountainous towards the south to the Beiras. Along the coastal Beiras, the topography becomes hillier with pine forests and a sandy coast. The capitol Lisbon in the central region and its surrounding area is known for its white rocks, olive fields, and open spaces. The Tagus basin divides the nation in half, with the yellow hills and cattle fields of the central region on the north bank and the beginnings of the Alentejo to the south. The Alentejo is a vast golden plain that extends south to the red cliffs and green hills of the Algarve. These conditions made the defense of Portugal difficult, the region was marked by eras of fortification building. Unlike many of their European counterparts, Portuguese castles were heavily influenced by the master-builders of Rome and Northern Africa. Even the early Celtic tribes of Portugal, the early Lusitanians, already fortified their villages within simple stone walls by this time. The Romans, who occupied Portugal for the next 400 years after this period, then built forts with high walls and strong towers to defend their towns. The Romans were the first to bring in organized military outposts in order to guard their domains. These outposts were usually built on existing fortified castros or defensible Neolithic/Paleolithic strongholds in the hills. Eventually, the Romans gradually built their centers based on their trade and/or commercial needs and abandoned many sites for places along rivers or lowland agricultural settlements. The outposts that remained continued to serve as sentries or outposts, while some points evolved into larger towns or cities that survived long after the Romans had retreated.
By the Middle Ages, Portugal was a crossroads of cultures, with hostile Moors to the south and rival Iberian kingdoms to the east. There were primarily two main periods of fortified castle construction: those built and defended by the Moors from Northern Africa, between the 8th and 13th centuries, and those built or maintained by Christian forces including the Kingdom of Portugal, after this period.
Moors
The Moors, Islamic peoples who had arrived in the Iberian Peninsula from Northern Africa around 711 A.D., conquering the Christian lands ruled by the Germanic Kingdoms of the peninsula, built strong castles and fortifications in many cities. They brought innovative stonework and heavily fortified gates to Portugal. Meanwhile, Northern European and English forts/castles were built with wood material during this period. Although many Portuguese medieval castles originated in the Islamic period, most of them were extensively remodeled after the Christian reconquest. One of the best-preserved is the Castle of Silves, in the ancient capital of the Al-Garb (today's Algarve). Built between the 8th and 13th centuries, the castle retains its walls and square-shaped towers from the Moorish period (including its 11th-century cisterns or water reservoirs). The old Moorish center of the city, the Almedina, was defended by a wall and several fortified towers and gates, parts of which are still preserved.