Mommy, Why was the Alphabet Invented?

Yesterday my 6 year old daughter asked me why someone invented the alphabet. I told her that long, long ago people used to communicate by speaking and drawing pictures. Then I mentioned that drawing a picture helps for some things, but there are just some things you can't communicate with a picture. As an example I asked her to suppose that I wanted her to clean her room and I drew her a picture of a messy room. I said that she might just think I wanted to draw a picture of her room and she may not know that I wanted her to clean her room. She seemed to understand and laughed. Then I told her that some smart person decided that if we had a system of symbols to represent sounds that words could be put down in writing. So that when we speak the sounds and put them together we make the words that we speak.