This volume has come to life as a result of the Research Project (HUM2009-07079) «La formación del paisaje medieval en el Norte Peninsular» (The formation of the Medieval landscape in the Northern Iberian Peninsula), funded by the Ministry of Science and Innovation, and its main aim is to analyse the main Early Medieval castles of the north-west quarter of the Iberian Peninsula, based on the most recent archaeological and historical researches. In this volume there are three main objectives:

1. To publish the results of several archaeological excavations carried out in Early Medieval castles of the north-western quadrant of the Iberian Peninsula. These had been studied as part of programmes of preventive and research projects carried out during the last years on various fortified sites, but those had only been partially published.
2. To propose some territorial syntheses of the current research projects for each of the areas of the region under study.
3. Lastly,to analyse the fortification process in the MiddleAges, based on primary documentation.

The resulting conclusions are multiple, because behind labels such as castles, hilltop settlements and fortifications, researchers are grouping together material and functional realities of diverse nature: from the big castles, located in the interior of the Peninsula and the edges of the plateau formed after the collapse of the Roman state, which serve as new axes for the local powers, up to the numerous small fortified enclosures of the Cantabrian range that emerge later in the period, together with towers and other hilltop settlements resulting of the incastellamento. And even if we find ourselves in the early stages of the study of these sites, the papers collected in this volume propose new topics and problems that may help us in future studies.