During the later Predynastic period in Egypt, circular huts were replaced by rectangular houses. Archaeological evidence for the appearance of these houses is extremely limited. It mainly consists of post holes and foundation slots, with little information about the structure above ground level. This model of a house, probably originally placed in a tomb, provides vital information about what the houses of this period looked like. Models of later periods show how houses changed over time.The battered walls curve inwards towards the top, suggesting that the structure was made of mud brick. This technique makes the wall stronger, and was still used for buildings until recent times. The archaeologist Flinders Petrie found remains of mud brick houses of this date at Naqada. The windows and door are set in the short walls of the structure, both with heavy wooden lintels. These let in both air and light. The windows were placed high in the wall to stop unwelcome visitors such as snakes and scorpions. The curved feature across the upper part of the doorway is probably a rolled up mat, which closed the entrance but allowed air into the house. The curved roof, only part of which survives, was probably constructed from palm fronds and other vegetation.