In general, the Cyclades are steep and rocky, though some Islands have stretches of coastal and interior plains. Although many of the islands appear to have had forests in ancient times, land clearing, shipbuilding, animal grazing, and the use of wood for fuel and house building have taken their toll, and today the islands are severely deforested and suffer from erosion by water and wind. Since prehistoric times, settlement seems to have followed a general pattern of nucleated villages (with some variation according to land tenure and kinship systems), the location being determined by the need for protection, shelter, and/or proximity to water and cultivable land. Each village is surrounded by cultivated fields, though some fields may be at a considerable distance from the village. Houses today are built of concrete block or reinforced concrete, but in the past houses were constructed of local stone, usually plastered inside and out, and whitewashed. Roofs were made of branches covered with packed earth or clay, or sometimes flat stone. On some islands pitched tile roofs are also found, though these are less characteristic of the Cyclades as a whole. Although "mosaic" floors are the norm today, one can still see the occasional traditional packed-earth floors in village homes. Aside from rafters, wood is rarely used in buildings except for shutters and trim (which may be painted in bright colors). There is generally one main town on each island, and this town today is often the port (though there may also be smaller secondary ports as well). In the past, villages were clustered for defense against frequent raids by pirates and Turks, and the main towns themselves (such as the port town of Naxos) were fortified or were situated inland for protection (as the now-deserted town of Exobourgos on Tinos). In some towns and villages remains of such fortifications with their thick exterior walls and small windows may still be seen. Nowadays, the nucleated village settlement pattern is being broken somewhat by the building of summer "country" houses, which may be located in fields outside the villages.