Plague pits have been archaeologically excavated during underground construction work. However, since the 1990s the site has been excavated repeatedly by archaeologists. Most of the tombs have been excavated. Other pits that formed the necropolis have also been excavated. The Saugeen mounds have not been excavated. The caves were possibly excavated during this period. The tomb itself has not yet been excavated. Its fossils have been excavated from Alaska to Mexico. Four main pits approximately deep have been excavated. However, these were not excavated but instead infilled with rubble. Ka's tomb was first excavated by Petrie in 1902. Thousands of bones have subsequently been excavated. Finally, landfill mining involves sites where landfills are excavated and processed. At Trafalgar Square, the station tunnels had been excavated. From the 1960s, stone churches have also been excavated in Slovakia.