While on a drive through rural Grundy and Harrison Counties, Missouri my wife and I noticed a couple of round stone structures set off in fields. I initally thought they were silo's until someome made a comment that they were old cistern's built by early pioneers. The source also thought that the cistern's were placed along wagon/horse trails or near towns. The ones I saw were in very isolated areas with no apparent roads, trails or towns near them. I was wondering if someone could tell me more about the history, construction and how they worked. Thanks! Jeff