Everyone keeps their most precious things in a safe place. We put diamonds and golden rings in a strongbox. Our money (for those who have more than a few notes) is stored in banks and lenders. This happens for all invidual properties. When a good is precious for a group of people (a company or a farm for instance) or even for a whole community, it is often kept in a huge structure: a silo. Water, oil, grain, coal, cement, food, sawdust and many more things are accumulated in beautiful, circular silos. All silos share the same external appearance. It is what they have inside that makes them unique. From the road you can only guess...