A pyramidion is the top or capstone of a pyramid or obelisk, made from a single block of stone. In antiquity pyramidia were referred to as bnbn.t. This associated the entire structure with the bnbn, the mound on which Atum settled after it had risen from the primordial water Nun. This mound was thought to have turned into a pyramid-shaped structure, after which the bnbn-stone was named. This stone was kept in a temple in Heliopolis, the centre of solar cult, as the place on which the first sun rays shone.
The use of pyramidia dates back to the Old Kingdom, when they were used as capstones on pyramids. These pyramidia were made separately and added onto the structure when it was finished, whereas the pyramidia of obelisks were integral parts of the monument. Most examples are made of a hard type of stone, often calcite, limestone, sandstone or even granite, sometimes covered in precious metal such as gold to reflect the sun light.
From the New Kingdom onwards, with the disappearance of the pyramid shape for royal tombs, pyramidia were added to private tombs as architectural elements. They were set on top of steep mud brick pyramid-shaped structures that were built on top of the funerary chapel, which gained in importance during the New Kingdom and became the most important element of the superstructure of the tomb. These pyramidia were still connected to the solar cult, as most of them bear decorations and texts referring to the sun god in its rising and setting incarnation.