This two-floor building of quite patty extent was built concurrently with the conventual minster before 1320.Its lower part served to store the bones exhumed out of the cemetery and the upper floor as a chapel. Originally there was a high hip roof without the gable and a western steeples finished off in lantern shape, where eternal light was on.

It was damaged during the Hussite Wars, the upper chapel was restored in 1661 and the project of the ossuary restoration and narthes extention was created by Jan Blažej Santini after 1710.According to the monastery tradition was the bone decoration arranged already in the 16th century. Jan Blažej Santini made to install a new decoration during the restoration of the complex, which was later in 1870 supplemented by the carver František Rint with many details assembled of bones, which covered the arch walling of the main room, stood in the niches or were part of the contents of the church. The ossuary at that time was in possession of Karl Schwarzenberg, who financially supported the project, therefore his generic coat of arms is situated above the stairway.

The most remarkable source in our archive is the watercolour painted by Jan Erazim Vocel, which shows the ossuary still in its baroque shape as the only one. The first photography of the decoration taken by Jindřich Dittrich are also very valuable.