The Brno Ossuary is the second largest ossuary in Europe. The town of Brno, located in the Czech Republic, was settled in the year of 1243. The discovery of the bodies occured quite recently and definitely by accident.
Before completing renovations in the small town, it is standard practice to complete a preliminary archeological dig. When the digging began in 2001, it turned up some 50,000 skeletons that were stuffed under the square into a medieval charnel. Once piled in neat rows, at some point water and mud had flooded the gigantic underground ossuary and jumbled thousands upon thousands of bones.
The bones are thought to be from the 1600 through the 1700s and are believed to have been moved from an old cemetery to make space for more burials. This is the case for most of the ossuaries and catacombs in Europe. It is the sheer amount of skulls, bones and skeletons that makes it the second largest ossuary in Europe, with the first being the Catacombs in Paris.
Because of the different colors on the bones, It is clear that many of the people died of various diseases. Though all the bones are tinted yellow, having never been exposed to sunlight, the extra yellow ones likely died of cholera, while the red tinted bones probably died from the plague.