Housing in Scotland includes all forms of built habitation in what is now Scotland, from the earliest period of human occupation to the present day. The oldest house in Scotland dates from the Mesolithic era. In the Neolithic era settled farming led to the construction of the first stone houses. There is also evidence from this period of large timber halls. In the Bronze Age there were cellular round crannogs (built on artificial islands) and hillforts that enclosed large settlements. In the Iron Age cellular houses begin to be replaced on the northern isles by simple Atlantic roundhouses, substantial circular buildings with a drystone construction. The largest constructions that date from this era are the circular brochs and duns and wheelhouses.