The Bicholim conflict, a war Wikipedia invented
2007
A detailed Wikipedia article described the Bicholim conflict, a 17th-century war between the Portuguese and the Maratha Empire, complete with a peace treaty. It held Good Article status for five years before an editor established that no such war took place. It stands as the most-cited example of how long a well-formatted fabrication can survive in a reference work.
Source: Wikipedia
Part of Pranks · Watch in the documentary