After printing was invented, knowledge was spread around the world by books. For many years, books were very expensive. Each one was written by hand, so very few books were produced. Today, books are produced quickly. They’re light, cheap and easy to get hold of. But the early books are now too valuable to be picked up and held in the hand, so here in the British Library, they were copied onto a computer a few years ago. Have a look at the screen here. You can turn the pages on the screen, without touching the real books.