The retainer system (military duties) in the ancient German society and the land loan system (land protection) in the later Roman Empire are often seen as the origin, and it is often explained that the two systems were combined to form feudalism.
古ゲルマン人社会の従士制度（軍事的奉仕）と、ローマ帝国末期の恩貸地制度（土地の保護）に起源を見いだし、これらが結びつき成立したと説明されることが多い。