Simultaneously with the spread of Christianity still another power began to trample on the liberties of the people. This was the power of the sword. In early times, before civilization had advanced enough to give everybody continuous employment, most people spent their leisure moments in making war. Hence the Swedish kings, whose duty it was to keep the peace, could accomplish that result only by having a large retinue of armed warriors at their command. The expense which this entailed was great. Meantime the crown estates had continually increased in number through merger of private estates of different kings, through crown succession to estates of foreigners dying without descendants in the realm, and through other sources. Some of the kings, therefore, devised the scheme of enlisting the influential aristocracy in their service by granting them fiefs in the crown estates, with right to all the crown incomes from the fief. This plan was eagerly caught at by the aristocrats, and before long nearly all the influential people in the realm were in the service of the king. Thus the position of royal courtier, which had formerly been a mark of servitude, was now counted an honor, the courtiers being now commonly known as magnates. About the year 1200 castles were first erected on some of the crown estates, and the magnates who held these castles as fiefs were not slow to take advantage of their power. Being already the most influential men in their provinces, and generally the county or provincial magistrates, they gradually usurped the right to govern the surrounding territory, not as magistrates of the people, but as grantees of the crown estates. Since these fiefs were not hereditary, the rights usurped by the holders of them passed, on the death of the grantees, to the crown, and in 1276 we find a king granting not only one of his royal castles, but also right of administration over the surrounding land. Thus, by continual enlargement of the royal fiefs, the authority of the provincial assemblies, and even of the county assemblies, was practically destroyed. Still, these assemblies continued to exist, and in them the poor landowners claimed the same rights as the more influential magnates. The magnates, as such, possessed no privileges, and were only powerful because of their wealth, which enabled them to become courtiers or warriors of the king. In 1280, however, a law was passed exempting all mounted courtiers from crown taxation. This law was the foundation of the nobility of Sweden. It divided the old landowners, formerly all equal, into two distinct classes,--the knights, who were the mounted warriors of the king; and the poorer landowners, on whom, together with the class of tenants, was cast the whole burden of taxation. With the progress of time, exemption from crown taxation was extended to the sons of knights unless, on reaching manhood, they failed to serve the king with horse.