Horizontal and vertical writing in East Asian scripts
Long ago, people used hieroglyphs. Hieroglyphs were very flexible characters. They were often written from left to right in the first line, and then right to left in the second line, and so on. This is called boustrophedon. A person can tell which direction to read by which direction the hieroglyphs of animals and people were facing. If the hieroglyphs were facing left, then the line must be read from left to right. If they were facing right, they must be read from right to left.