This article aims to analyse one of the most fascinating primary sources of the history of law of the European Middle Ages: The Mirror Saxon, made around 1225 in the Duchy of the (Lower) Saxony in the Holy Roman Empire, in particular working with the manuscript illustrated from the Heidelberg University Library of 1300 approximately. The fascinating thing about is that the unique Images allow a direct look at the legal perceptions of the time in question, through interpretations of historical illustrator. The analysis will focus on the rules that belongs, according to the systematic logic of today, to the public law, within an integral text that contains some rules which now we would consider as civil law. The main idea is to make visible and understandable several key pillars of statehood and legal thought of this era. In 16 sub-chapters, it begins with the theoretical and methodological introduction. The second subchapter will present the “book of law” and its author, to problematize, the third the context and process of law-making. Fourth, the division of the material discussed in the categories of territorial and feudal law. Successive sub-chapters are dedicated to examples of public law Saxon: the fifth introduces the vision of the double-head of medieval Europe with Emperor and Pope; the sixth discusses the theory of translatio imperii and Roman identity coopted in the medieval State; the seventh analyses the difficult search for the public peace. Next, the eighth section is dedicated to the phenomenon of elective monarchy and the board of the electors. Ninth, the shield of the army and the feudal constitution is investigated. The tenth section holds the public functions of the oath. Eleventh, the theme will be the relationship between nature and power in the Saxon Middle Ages. Twelfth, he wonders concepts of human dignity at the time. In the Thirteenth, the courts of justice are expounded, to enter the fourteenth subchapter about the public criminal law of the thirteenth century. In fifteenth place, the text is dedicated to European diffusion and trajectory of six centuries of Saxon Mirror, to finish with some concluding considerations.