Archaeological forgery is the manufacture of supposedly ancient items that are sold to the antiquities market and may even end up in the collections of museums. It is related to art forgery. A string of archaeological forgeries have usually followed news of prominent archaeological excavations. Historically, famous excavations like those in Crete, the Valley of the Kings in Egypt and Pompeii have caused the appearance of a number of forgeries supposedly spirited away from the dig. Those have been usually presented in the open market but some have also ended up in museum collections and as objects of serious historical study. In recent times, forgeries of pre-Columbian pottery from South America have been very common. Other popular examples include Ancient Egyptian earthenware and supposed ancient Greek cheese. There have also been paleontological forgeries like the archaeoraptor or the Piltdown Man skull. Most archaeological forgeries are made for reasons similar to art forgeries – for financial gain. The monetary value of an item that is thought to be thousands of years old is higher than if the item were sold as a souvenir. However, archaeological or paleontological forgers may have other motives; they may try to manufacture proof for their point of view or favorite theory (or against a point of view/theory they dislike), or to gain increased fame and prestige for themselves. If the intention is to create "proof" for religious history, it is considered pious fraud. Investigators of archaeological forgery rely on the tools of archaeology in general. Since the age of the object is usually the most significant detail, they try to use radiocarbon dating or neutron activation analysis to find out the real age of the object. Some historians and archaeologists have strongly criticized the antiquities trade for putting profit and art collecting before scientific accuracy and veracity. This, in effect, favours the archaeological forgery. Allegedly, some of the items in prominent museum collections are of dubious or at least of unknown origin.