The nuraghe (, ; plural: Logudorese Sardinian , Campidanese Sardinian , Italian ), or also nurhag in English, is the main type of ancient megalithic edifice found in Sardinia, developed during the Nuragic Age between 1900 and 730 B.C. Today it has come to be the symbol of Sardinia and its distinctive culture known as the Nuragic civilization. More than 7,000 nuraghes have been found, though archeologists believe that originally there were more than 10,000. Etymology According to the Oxford English Dictionary the etymology is "uncertain and disputed": "The word is perhaps related to the Sardinian place names Nurra, Nurri, Nurru, and to Sardinian nurra 'heap of stones, cavity in earth' (although these senses are difficult to reconcile). A connection with the Semitic base of Arabic nūr 'light, fire, etc.' is now generally rejected." The Latin word murus ('wall') may be related to it, being a result of the derivation: murus–*muraghe–nuraghe. However, such theory is debated. An etymological theory suggests a Proto-Basque origin by the term *nur (stone) with the common -ak plural ending; the Paleo-Sardinian suffix -ake, also found in some Indo-European languages such as Latin and Greek. Another possible explanation is that the term nuraghe came from the name of the Iberian mythological hero Norax, and the root *nur would be an adaptation of the Indo-European root *nor. General layout The typical nuraghe is situated in areas where previous prehistoric Sardinian cultures had been distributed, that is not far from alluvial plains (though few nuraghes appear in plains currently as they were destroyed by human activities such as agriculture, dams, road building etc.) and has the outer shape of a truncated conical tower, thus resembling a medieval tower, with a tholos-like vault inside. The structure's walls consist of three components: an outer layer (tilted inwards and made of many layers of stones whose size diminishes with increasing height: mostly, lower layers consist of rubble masonry, while upper layers tend to be of ashlar masonry); an inner layer, made of smaller stones (to form a corbelled dome of the bullet-shaped tholos type, and where ashlar masonry is used more frequently); and an intermediate layer of very small pieces and dirt, which makes the whole construction very sturdy: it stands only by virtue of the weight of its stones, which may each amount to several tons. Some nuraghes are about 20 meters (60 ft) in height, the tallest one known,