Void Century
The Void Century is a century-long gap in recorded and archaeological history, the study of which is forbidden by the World Government. These events occurred 900 to 800 years before the current storyline. It was hinted at during the Skypiea arc; the dates were seen in Robin's flashback. This period became known as the Void Century because there is nothing left to acknowledge anything that happened in it, aside from the poneglyphs which are written in a language that few know how to read. However, it causes a problem with the known histories of the world as nothing ties up because of that missing period. Though many seem to know there is a gap in the historical record, virtually everyone is unaware that filling in this gap is possible. For example, Nefertari Cobra, after being told by Nico Robin about this missing period, was completely shocked that a way to "tie the threads of history together" existed. The fact that filling the gap is possible was proven when "...