The Palermo Stone is a fragment of a wall, that was inscribed on both sides with an overview of mostly ritual events that occurred during the first five dynasties. Several other fragments of that same wall (or a copy of it?) have been found as well. The Palermo Stone is the largest piece of the wall is now on display at Palermo, hence its name.
A second large piece and four smaller fragments are in the Cairo Museum (Cairo Fragments 1 to 5) and one small fragment is in the University College of London (London Fragment).
It is not certain that all seven known pieces derive from the same original, as all fragments were found on the antiquities market. Only one small Cairo fragment seems to have been traced to Memphis, but some other fragments are believed to have originated in Middle Egypt. The differences in thickness of the fragments, may also be an indication that there were several originals, but thusfar, none of the fragments contains a partial or full copy of one or more of the other fragments.
The original to which the Palermo Stone belonged, is believed to have been approximately 2.2 meters long, 0.61 meters high and 6.5 cm thick. It is generally accepted, but not proven, that the large Cairo Fragment, may have belonged to the same original.
It is inscribed on both sides with a list of kings from Predynastic Egypt to the middle of the 5th Dynasty. From the 4th Dynasty on, the list also contains the foundations and offerings made by the kings. It is thus highly valuable in the study of the early history of Ancient Egypt.
The exact creation date is not known, the earliest possible date being the middle of the 5th Dynasty. Some Egyptologists have seen differences in the style of hieroglyphs in different year cells, which has led them to believe that the stone or stones may have been carved at different times, perhaps even updated on a regular basis. If this is correct, then at least the later parts of the stone(s) were carved shortly after the reported events.
On the other hand, the way the stone has been carved -lightly incised signs on a black stone- is reminiscent of an artistic style that came into vogue during the 25th Dynasty, suggesting that the Palermo Stone and related fragments may perhaps not be dated earlier than this dynasty.
The fact that for the Early Dynastic kings, their actual Horus-names were used, rather than their fictive Prenomens of Nomens, as is the case on the Turin Kinglist, could support the thesis that, regardless of the creation date of the Palermo Stone, the composers of this document had access to original sources. Maybe the Palermo Stone is just a late copy of an original that was created during the Old Kingdom.
Another question that needs to be addressed is the purpose of the Palermo Stone and related fragments. Did the composers intend to actually compile historical information, as seems to have been the case with the Turin Kinglist? Or was the stone originally located in a temple, serving a religious or propagandistic purpose? In the latter case, the historic value attached to this document may have been overestimated.