This was a really interesting incident. There is a <i>ton</i> of plagiarism on Quora, the vast majority of it incredibly obvious. It doesn't address the question and looks as if it were addressed to a different target audience. A momentary Google search turns up the source. (Often, it's plagiarized directly from Wikipedia, without even editing out the footnote links.)<p>This was something different. It would have been easy to spot that this person was plagiarizing their text, if it had occurred to you to look for it. But they were writing both the question and the answer, and the answers seemed to actually address the question. They were scholarly and well-written, and didn't set off the same alarms that the vast majority of plagiarism does.<p>It's surprising that more people didn't think to check earlier. If nothing else, the questions seemed off; nobody would think to ask questions like that for which this guy always had exactly the right answer. The accounts asking them were new, so it smelled of sock-puppet.<p>It was propped up by a fair number of real historians who didn't seem to think anything was off, and that caused a web-of-trust failure. Individuals who might have smelled a rat were lulled by the informed people holding intelligent conversations in the comments, distracting from the suspicious source.<p>Once somebody thought to inquire, it was obvious. And the whole thing seems unique: it took more intelligence and thought to pull this off than most plagiarists put into it. This has not been repeated -- as far as anybody can tell.