Mozart wasn't buried in a pauper's grave as most people understand them, it's a common misconception since the definition has changed in modern times.

Mozart was buried in a common grave, or in other words a grave that would be dug up and reused after 10 years or so. The custom was common for most people at the time. Private Graves were reserved only for the aristocracy and clergy at the time.

There were several types of common graves. A pauper's grave was paid for using public funds which was considered in bad taste and a common grave was paid for by the family. The actual burials were exactly the same with the one exception. Most people were buried in the manner in which Mozart was buried. Indeed the reason no one has been able to pinpoint his exact location is because so many others were buried in this manner.

The exception to the common grave was an "inscription grave". With this option the number of people in a plot were limited and they were given a headstone. These graves were subject to excavation, but were given low priority for it, which is to mean that many became de facto private graves. Certainly this is the type of grave his widow would have liked him to have and she did spend time trying to find his plot to make that happen once his status rose after his death with no success.

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