Historical knowledge is gained empirically, ie it is the result of source studies. The historical material as the subject of historical research includes all kinds of human tradition, written and non-written: documentary texts (documents, files, contracts, correspondence, tax registers, etc.), narrative texts that contain the reproduction and views of the past (chronicles, Biographies, memoirs, travel descriptions, etc.), objects (graves, streets, coins, buildings, works of art, etc.), facts (law, names, language, calendar, etc.).