For natural reasons it is somewhat difficult to find remnants of prehistoric dwellings in Denmark. Our early forefathers utilized perishable materials in their house building, such as wood and straw. They made use also of clay and sod and, to a small extent, of natural stones. However, Denmark is one of the most intensely cultivated lands of Europe. The plough has been almost everywhere; and when the ploughshare has gone through the remnants of a hut of sod and clay the site is generally spoilt for the archaeologist. As a rule, we cannot expect to find any house-site intact unless it has been covered with a layer of soil, sufficient for protection against the plough.While our knowledge of the prehistoric dwellings is, on the whole, very incomplete, we know something about the dwellings of the Iron Age for the cultural deposits are comparatively thick. It was probably not until the Early Iron Age—i.e. the La Tène and Roman periods—that agriculture reached such a stage of development that successive generations might dwell on the same site. Our best finds are from the northern part of Jutland. In Thy and Himmerland there are a number of deposits of Roman and the pre-Roman Iron Age with a depth of 1–2 m., containing several dwelling-sites above each other. Evidently, there existed in northern Jutland small village-sites, in the Roman period and probably somewhat earlier, of permanent habitation and occupied for several generations.