Megalithism, specially in the form of burials in dolmens, was widespread. Megalithism The Basque Country has multitude of megaliths, described as dolmens or mounds, sometimes confusingly. They are in any case burials of collective nature, placed in spots of great visibility, often on top of mountain ridges. The materials used are always of local origin. Dolmens are the most typical, being formed by a chamber delimited by flat stones, often quite large, covered by another stone as roof. The monument was then covered by stones and earth, making up a mound. The chambers are of two types: simple or with corridor. The first are more common, while the latter are limited to the Ebro valley area. Dolmens are also classified by their size, normally the largest ones being in lowland areas and the smaller ones in mountain zones. This was probably a function of the number of people available to build the monument. The burial classified as mounds lack of chamber but were otherwise used like dolmens for collective burials. There are around 800 dolmens known in The Basque Country and c. 500 mounds, though some of these could be dolmens as well, in wait of excavation. Only a few Basque dolmens have clear stratigraphies, due to the usage of removing older remains to make room for new burials. In spite of this difficulty, it's known that megalithic burial customs arrived to the Basque Country in the late Neolithic being very frequently used in the Chalcolithic and Early Bronze Age, and, in the case of some mounds, as late as the Iron Age. Other megalithic structures, such as standing stones (menhirs) and stone circles (cromlechs) seem to belong to later periods, specifically the Iron Age. Bronze Age The Bronze Age spanned from c. 1700 to c. 700 BCE. It is largely a continuity of the previous period. Gradually bronze tools replaced stone and copper ones and we can find the first fortifications, that would become very common in the last centuries of this period. This age is divided in three subperiods: Early Bronze Age (c. 1700-1500 BCE): occasional use of bronze, larger pots. Middle Bronze Age (c. 1500-1300 BCE): generalization of bronze tools, first fortifications, first decoration of pottery (cordons). Late Bronze Age (c. 1300-700 BCE): bronze arrow points, variety of pottery decoration, spread of fortifications. Megalithism continued for most of the period, yet external influences became increasingly noticeable since