Since there are several threads about the "most important..." of many sorts, it is perhaps time for discussing some of the most important human achievements - inventions, innovations, artifacts, of all time. I think it is - at least - as great as anything of the last centuries, if not even more, and can be compared to agriculture, writing, fire or the wheel. It is anything artificial mean of transportation on water, wether raft, boat, ship. I can hardly see anything like human societies as we know them, even less "civilization" could develop without. Is that fully appreciated in most history books?