Casimir I the Restorer
Unlike Western Europe, in Poland, the did not emerge exclusively from the feudal class of knights but stemmed in great part from earlier Slavic local rulers and free warriors and mercenaries. Rulers often hired these free warriors and mercenaries to form military units () and eventually, in the 11th century during the time of Casimir I the Restorer with the development of feudalism, armies paid by the Prince were replaced by knights that were paid in land. Much written evidence from the Middle Ages demonstrates how some elements of the Polish nobility did emerge from former Slavic rulers that were included in the ranks of the knightly class under the terms of the chivalric law () and .