In the eleventh and twelfth centuries there is no doubt that the inhabitants of Northern Spain, under some of the petty kings, enjoyed more constitutional liberty than any other people in Europe; that their institutions generally, and especially their municipal privileges, were more in accordance with the ideas of modern freedom and self-government than those of any other nation at that date. The feudal system never attained in Northern Spain, except in parts of Catalonia, the systematic development, and the organized oppression of the lower classes, which it reached in many other parts of Europe. The peculiar institution of "_behetria_," which prevailed in Leon and the Castiles, and by which a serf was free to go whither he would "from sea to sea," with all his goods, and to put himself under any lord he chose, was of itself an almost sufficient check to excessive tyranny by the nobles. The old Roman municipal organization, of the towns had been preserved by tradition throughout the whole of the Visigothic times down to 711, nor had the practical working completely died out at the epoch of the early reconquest of the north. Hence many of the charters or "_fueros_" granted to the towns and cities by the kings are evidently founded on a recollection of former institutions, modified according to the necessities of the times. Thus the charter of Leon (1020) expressly allows exemption from all arbitrary exactions, and grants the free election of the _Alcalde_, and of the municipal council, with only the appointment of the judges by the king. By the _fuero_ of Arganzon (1191) it is expressly stated that if these royal officers overpassed their duties, it would be lawful to kill them without incurring any responsibility. Similar but still more strongly-worded clauses are found in all the Basque _fueros_, and in the coronation oath of Aragon.