Martin Hirshberg, age 12, of Sparks, Nev., for his question:

WHEN WAS THE FIRST HOUSE BUILT?

We don't know when man built his first house, but we know it was back in prehistoric days before records were kept.

The first shelters were in trees. Men learned that tall trees offered protection from animals and also kept off some of the rain. Later, they learned to pile branches to make crude shelters from the wind. Still later, men lived in caves.

Finally, men learned to make simple tools. At first, the tools were made of stone. Later they were made of metal. The tools helped men build better shelters.

Men learned to pile up stones to make a shelter where there were few trees. And they also learned to form clay into small blocks that could be dried in the sun. Shelters were then built by piling up these blocks on each other.

Before 4000 B.C., lake dwelling people learned to make their houses over water. They drove heavy logs into the lake bottom near the shore and built platforms on the logs.

Ancient Egyptians started building flat topped homes of sun dried brick around 3000 B.C. The Assyrians also adopted this method of building about 2500 B.C. But the Assyrians discovered that putting bricks into fire made them harder and stronger.

The ancient Greeks made stone houses with slanted roofs. They were the first to put doors in their buildings.

The Romans copied many of the Greek ideas, but they were the first to put in central heating. The Romans put rows of earthenware pipes under the floor and ran hot air or hot water through them to heat the floors and rooms.

The Romans also added small windows to their walls and were the first to use glass windowpanes.

German and Scandinavian tribes later introduced buildings with frameworks of heavy wooden timbers.

Early Northmen from German and Scandinavian tribes built roofs with high peaks, which they covered with layers of bark and then layers of grass sod. They also dug ditches and built earthen walls around their homes to protect them from animals.

As the Middle Ages came in, castles were built with thick stone walls, water filled moats and drawbridges.

Around 1300, European nobles became the first to build fireplaces in their castles.

About 1400, Europeans began to build half timbered houses with brick or stone foundations. Tree trunks were placed at each corner of the house, with beams placed between the trunks. Walls were covered with lath and then plastered with a mixture of clay and straw.

By the 1500s, people were building half timbered houses three or four stories high.