Henry, the abbot of the Cistercian monastery in Sedlec, was sent to the Palestine (Holy Land) by King Otakar II of Bohemia in 1278. When he returned, he brought with him a small amount of earth he had removed from Golgotha and sprinkled it over the abbey cemetery. The word of this pious act soon spread and the cemetery in Sedlec became a desirable burial site throughout Central Europe. During the Black Death in the mid 14th century, and after the Hussite Wars in the early 15th century, many thousands of people were buried there and the cemetery had to be greatly enlarged.
Around 1400 a Gothic church was built in the center of the cemetery with a vaulted upper level and a lower chapel to be used as an ossuary for the mass graves unearthed during construction, or simply slated for demolition to make room for new burials. After 1511 the task of exhuming skeletons and stacking their bones in the chapel was, according to legend, given to a half-blind monk of the order.
Between 1703 and 1710 a new entrance was constructed to support the front wall, which was leaning outward, and the upper chapel was rebuilt. This work, in the Czech Baroque style, was designed by Jan Santini Aichel.
In 1870, František Rint, a woodcarver, was employed by the Schwarzenberg family to put the bone heaps into order. The macabre result of his effort speaks for itself. Four enormous bell-shaped mounds occupy the corners of the chapel. An enormous chandelier of bones, which contains at least one of every bone in the human body, hangs from the center of the nave with garlands of skulls draping the vault. Other works include piers and monstrances flanking the altar, a large Schwarzenberg coat-of-arms, and the signature of Rint, also executed in bone, on the wall near the entrance. (Text from Wikipedia).