The Hohenstaufen rulers increasingly lent land to ministerialia , formerly non-free service men, who Frederick hoped would be more reliable than dukes. Initially used mainly for war services, this new class of people would form the basis for the later knights , another basis of imperial power. A further important constitutional move at Roncaglia was the establishment of a new peace mechanism for the entire empire, the Landfrieden , with the first imperial one being issued in 1103 under Henry IV at Mainz .   This was an attempt to abolish private feuds, between the many dukes and other people, and to tie the Emperor's subordinates to a legal system of jurisdiction and public prosecution of criminal acts – a predecessor of the modern concept of " rule of law ". Another new concept of the time was the systematic foundation of new cities by the Emperor and by the local dukes. These were partly caused by the explosion in population, and they also concentrated economic power at strategic locations. Before this, cities had only existed in the form of old Roman foundations or older bishoprics. Cities that were founded in the 12th century include Freiburg , possibly the economic model for many later cities, and Munich .
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